Small molecule inhibitors of cav3.2 activity and uses thereof

ABSTRACT

This invention is in the field of medicinal chemistry. In particular, the invention relates to a new class of small-molecules having a piperazine or piperidine structure which function as inhibitors of the CaV3.2 voltage gated calcium channel activity (e.g., depolarization-induced calcium influx), and their use as therapeutics for the treatment and/or prevention of CaV3.2 related pain e g., HIV-associated peripheral sensory neuropathy, chemotherapy-induced peripheral neuropathy (CIPN), spinal nerve ligation (SNL) induced neuropathy) and related conditions.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of U.S. Provisional Application No. 63/023,672, filed May 12, 2020, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention is in the field of medicinal chemistry. In particular, the invention relates to a new class of small-molecules having a piperazine or piperidine structure which function as inhibitors of the CaV3.2 voltage gated calcium channel activity (e.g., depolarization-induced calcium influx), and their use as therapeutics for the treatment and/or prevention of CaV3.2 related pain (e.g., HIV-associated peripheral sensory neuropathy, chemotherapy-induced peripheral neuropathy (CIPN), spinal nerve ligation (SNL) induced neuropathy) and related conditions.

INTRODUCTION

Neuropathic pain is a major health burden [27]. Despite intense research on the topic, very limited non-opioid treatments are available as alternatives. A failure to develop new drugs to combat pain is primarily because neuropathic pain is a complicated disease that can originate from many different types of injuries (nerve injury, chemotherapy [70], human immunodeficiency virus—HIV—infection [1] and others) and whose establishment involves central and peripheral systems. While neuropathic pain is a multisystemic disease, spinal block has been clinically demonstrated to curb neuropathic pain in patients [32]. Thus, targeting molecular components of spinal transmission is a valid therapeutic strategy for the treatment of chronic neuropathic pain [8] as evidenced by the N-type voltage gated calcium channel (CaV2.2) blocker Prialt® [82].

Ion channels regulating afferent fiber excitability and synaptic function in the spinal dorsal horn are prime targets for the treatment of neuropathic pain [81]. One of these channels is the T-type Ca²⁺ channel [9]. These voltage-gated ion channels have a half activation voltage of ˜−45 mV [78], thus their contribution to the initiation of an action potential precedes the contribution of Na⁺ channels. The family of T-type Ca²⁺ channels contain three isoforms in mammals, CaV3.1, CaV3.2 and CaV3.3 with distinct expression pattern in tissues [41; 43]. In dorsal root ganglia (DRG) neurons, the predominant CaV3 channel isoform involved in pain signaling is CaV3.2 [4; 6]. CaV3.2 expression is restricted to the nociceptive Aδ- and C-low-threshold mechanoreceptors (LTMRs)[22]. CaV3.2 expression is increased following nerve injury [26]. Cav3.2 activity is also increased in paclitaxel-induced peripheral neuropathy [21; 58; 65; 87]. A specific role of CaV3.2 in pain was demonstrated by the observation that silencing this channel in DRG neurons reversed neuropathic pain in rats while silencing CaV3.1 or CaV3.3 did not [6]. Further evidence in support of CaV3 channels as important therapeutic targets for pain comes from studies of the T-type Ca²⁺ channels inhibitors ethosuximide [13; 31; 69], mibefradil, TTA-A2 or TTA-P2 [14; 77]—all of which reverse experimental neuropathic pain in rodents. However, clinical trials using T-type Ca²⁺ channel blockers for pain, such as ABT-639 [77] and MK-8998 [19], failed to meet the expected clinical endpoints. This may have been due to lack of selectivity for CaV3.2 leading to dose limitations. Another promising compound that may advance to clinic is Z944 [42; 80], but this molecule targets all CaV3 isoforms and may have the same clinical limitations as its predecessors.

Thus, there is a need for a specific CaV3.2 blocker.

The present invention addresses this need.

SUMMARY OF THE INVENTION

It has been shown before that a natural compound betulinic acid

(3β)-3-Hydroxy-lup-20(29)-en-28-oic acid), preferentially targets CaV3.2 and could reverse a could reverse allodynia in the paclitaxel induced peripheral neuropathy and HIV related sensory neuropathy models [3].

In searching for selective CaV3.2 T-type calcium channel blockers, experiments conducted during the course of developing embodiments for the present invention first performed a screening of an in-house chemical library using Fura 2-AM based ratiometric calcium-imaging assay. One hit compound, 5aa

see FIG. 1B) was identified to inhibit ˜50% of the Ca₂₊ influx when DRGs were depolarized with 40 mM KCl. Subsequent structure-activity relationship studies led to a more potent analog 5bk

see FIG. 1B). The T-type calcium channel block of 5bk was further confirmed in whole-cell patch clamp assays in rat DRGs, where pharmacological isolation of T-type currents leads to a concentration-dependent inhibition with an IC₅₀ of 4.2±0.6 μM. By silencing each of the CaV3 channels, it was found that 5bk could selectively inhibit CaV3.2. 5bk was shown to reverse mechanical allodynia in neuropathic—Chemotherapy-(paclitaxel) and HIV-induced—pain. 5bk inhibited spontaneous excitatory post-synaptic currents via actions presynaptically and inhibited release of the pronociceptive neurotransmitter calcitonin gene related peptide (CGRP). As 5bk did not affect locomotion or anxiety and was without action on opioid receptors, it appears to be a promising, safe, and non-opioid candidate for the treatment of neuropathic pain by virtue of its selective block of CaV3.2 T-type calcium channels.

Accordingly, the present invention relates to a new class of small-molecules having a piperazine or piperidine structure which function as inhibitors of the CaV3.2 voltage gated calcium channel activity (e.g., depolarization-induced calcium influx), and their use as therapeutics for the treatment and/or prevention of CaV3.2 related pain (e.g., HIV-associated peripheral sensory neuropathy, chemotherapy-induced peripheral neuropathy (CIPN), spinal nerve ligation (SNL) induced neuropathy) and related conditions.

Certain piperazine or piperidine (or similar) compounds of the present invention may exist as stereoisomers including optical isomers. The invention includes all stereoisomers, both as pure individual stereoisomer preparations and enriched preparations of each, and both the racemic mixtures of such stereoisomers as well as the individual diastereomers and enantiomers that may be separated according to methods that are well known to those of skill in the art.

In a particular embodiment, compounds encompassed within Formula I are provided:

including pharmaceutically acceptable salts, solvates, and/or prodrugs thereof.

Formula I is not limited to a particular chemical moiety for X, R1, R2, and R3. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit CaV3.2 voltage gated calcium channel activity. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit depolarization-induced calcium influx related to CaV3.2 voltage gated calcium channel activity. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit, prevent and/or ameliorate neuropathy pain related to CaV3.2 activity. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit, prevent and/or ameliorate pain related to CaV3.2 activity. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit, prevent and/or ameliorate pain related to HIV-associated peripheral sensory neuropathy. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit, prevent and/or ameliorate pain related to chemotherapy-induced peripheral neuropathy (CIPN). In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit, prevent and/or ameliorate pain related to spinal nerve ligation (SNL) induced neuropathy. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit spontaneous excitatory post-synaptic currents via actions presynaptically. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit release of the pronociceptive neurotransmitter calcitonin gene related peptide (CGRP).

In some embodiments, X is C thereby rendering the compound a piperidine based compound.

In some embodiments, X is N thereby rendering the compound a piperazine based compound.

In some embodiments, R1 is selected from

In some embodiments, R1 is hydrogen.

In some embodiments, R2 is selected from

In some embodiments, R2 is hydrogen.

In some embodiments, R3 is selected from

In some embodiments, R3 is hydrogen.

In some embodiments, the compound is recited in FIG. 1B.

The invention further provides processes for preparing any of the compounds of the present invention.

The CaV3.2 inhibitors described herein can be considered as potential therapeutics for the treatment, prevention, and/or amelioration of conditions characterized with pain related CaV3.2 activity (e.g., pain related to general neuropathy; pain related to diabetes related neuropathy; pain related to HIV-associated peripheral sensory neuropathy; inhibiting, preventing and/or ameliorating pain related to chemotherapy-induced peripheral neuropathy (CIPN); inhibiting, preventing and/or ameliorating pain related to spinal nerve ligation (SNL) induced neuropathy).

The invention also provides pharmaceutical compositions comprising the compounds of the invention in a pharmaceutically acceptable carrier.

The invention also provides kits comprising a compound of the invention and instructions for administering the compound to an animal. The kits may optionally contain other therapeutic agents, e.g., other agents useful in treating, preventing and/or ameliorating pain related to CaV3.2 activity.

The present disclosure further provides bifunctional compounds that function to recruit endogenous proteins to an E3 Ubiquitin Ligase for degradation, and methods of using the same. In particular, the present disclosure provides bifunctional or proteolysis targeting chimeric (PROTAC) compounds, which find utility as modulators of targeted ubiquitination of a variety of polypeptides and other proteins, which are then degraded and/or otherwise inhibited. An exemplary advantage of the compounds provided herein is that a broad range of pharmacological activities is possible, consistent with the degradation/inhibition of targeted polypeptides from virtually any protein class or family. In addition, the description provides methods of using an effective amount of the compounds as described herein for the treatment, prevention and/or amelioration of pain related to CaV3.2 activity, or inhibition of CaV3.2 activity.

In an additional aspect, the disclosure provides bifunctional or PROTAC compounds, which comprise an E3 Ubiquitin Ligase binding moiety (e.g., a ligand for an E3 Ubquitin Ligase or “ULM” group), and a moiety that binds a target protein (e.g., a protein/polypeptide targeting ligand or “PTM” group) (e.g., CaV3.2) such that the target protein/polypeptide is placed in proximity to the ubiquitin ligase to effect degradation (and inhibition) of that protein (e.g., inhibit CaV3.2 activity). In certain embodiments, the PTM is any of the compounds as described herein showing inhibitory activity against CaV3.2 activity. In some embodiments, the ULM is a VHL, cereblon, mouse double minute 2 (MDM2), and/or inhibitor of apoptosis protein (IAP) E3 ligase binding moiety. For example, the structure of the bifunctional compound can be depicted as PTM-ULM.

The respective positions of the PTM and ULM moieties, as well as their number as illustrated herein, is provided by way of example only and is not intended to limit the compounds in any way. As would be understood by the skilled artisan, the bifunctional compounds as described herein can be synthesized such that the number and position of the respective functional moieties can be varied as desired.

In certain embodiments, the bifunctional compound further comprises a chemical linker (“L”). In this example, the structure of the bifunctional compound can be depicted as PTM-L-ULM, where PTM is a protein/polypeptide targeting moiety (e.g., any of the compounds as described herein showing inhibitory activity against CaV3.2 activity), L is a linker, and ULM is a VHL, cereblon, MDM2, or IAP E3 ligase binding moiety binding moiety.

Such embodiments are not limited to a specific type of linker. In some embodiments, the linker group is optionally substituted (poly)ethyleneglycol having between 1 and about 100 ethylene glycol units, between about 1 and about 50 ethylene glycol units, between 1 and about 25 ethylene glycol units, between about 1 and 10 ethylene glycol units, between 1 and about 8 ethylene glycol units and 1 and 6 ethylene glycol units, between 2 and 4 ethylene glycol units, or optionally substituted alkyl groups interdispersed with optionally substituted, O, N, S, P or Si atoms. In certain embodiments, the linker is substituted with an aryl, phenyl, benzyl, alkyl, alkylene, or heterocycle group. In certain embodiments, the linker may be asymmetric or symmetrical. In some embodiments, the linker is a substituted or unsubstituted polyethylene glycol group ranging in size from about 1 to about 12 ethylene glycol units, between 1 and about 10 ethylene glycol units, about 2 about 6 ethylene glycol units, between about 2 and 5 ethylene glycol units, between about 2 and 4 ethylene glycol units.

The ULM group and PTM group may be covalently linked to the linker group through any group which is appropriate and stable to the chemistry of the linker. In exemplary aspects of the present invention, the linker is independently covalently bonded to the ULM group and the PTM group in certain embodiments through an amide, ester, thioester, keto group, carbamate (urethane), carbon or ether, each of which groups may be inserted anywhere on the ULM group and PTM group to provide maximum binding of the ULM group on the ubiquitin ligase and the PTM group on the target protein to be degraded. In certain aspects where the PTM group is a ULM group, the target protein for degradation may be the ubiquitin ligase itself. In certain exemplary aspects, the linker may be linked to an optionally substituted alkyl, alkylene, alkene or alkyne group, an aryl group or a heterocyclic group on the ULM and/or PTM groups.

In certain embodiments, the compounds as described herein comprise multiple ULMs, multiple PTMs, multiple chemical linkers, or any combinations thereof.

In some embodiments, the present invention provides a method of ubiquitinating/degrading CaV3.2 activity in a cell comprising administering a bifunctional compound as described herein comprising an ULM and a PTM, in certain embodiments linked through a linker moiety, as otherwise described herein, wherein the ULM is coupled to the PTM and wherein the ULM recognizes a ubiquitin pathway protein and the PTM recognizes the target protein such that degradation of the target protein occurs when the target protein is placed in proximity to the ubiquitin ligase, thus resulting in degradation/inhibition of the effects of the target protein and the control of protein levels. The control of protein levels afforded by the present invention provides treatment of a disease state or condition, which is modulated through the target protein by lowering the level of that protein in the cells of a patient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-B: Synthesis of compounds by the Ugi-Azide four-component reaction. (A) Synthesis methodology. (B) List of compounds synthesized and tested. 5bk is also referred to as UAWJ111.

FIG. 2A-B: (A) List of FDA-approved oral drugs that share similar structural features with 5bk. (B) Calculated ADME properties by Glide QikProp.

FIG. 3A-E: Primary screening using depolarization evoked Ca2+ influx in DRG neurons identifies several antagonists of low and high voltage-activated calcium channels. Peak calcium responses of sensory neurons incubated overnight with 20 μM of the indicated compounds in response to 40 mM KCl (A) or 90 mM KCl (B) and normalized to 0.01% DMSO-treated control. N>78 neurons per condition from at least 3-4 rats each. Representative time courses of the change in 340 nm/380 nm ratio for the response of 4 representative neurons imaged in a preparation treated with 0.01% DMSO or 5bk. Because an increase in intracellular calcium induces an increase in 340-nm emission and a decrease in 380-nm emission, the simultaneous increase in 340 nm and decrease in 380-nm fluorescence emission associated with application of KCl is indicative an increase in intracellular calcium. KCl was added at the time indicated by the arrow. (C) The structure of 5bk is shown. (D) Scatter bar graph shows peak calcium responses of sensory neurons in response to a 40 mM KCl challenge. Neurons were incubated with vehicle (0.01% DMSO) or a 20 μM concentration of 5bk for various period of time as indicated: acutely (less than 5 min), 30 min, 2 hours, or 12-18 hours (overnight). (E) Concentration response curve for 5bk inhibition of calcium influx in response to a 40 mM KCl challenge; neurons were treated with vehicle (0.01% DMSO) or a 20 μM concentration of 5bk overnight in this experiment. P values of comparisons between treatments are as indicated; see statistical analysis described in Table 1.

FIG. 4A-I: Acute (<10 min) treatment with 5bk does not inhibit T-Type Ca²⁺ currents in dorsal root ganglion (DRG) sensory neuron. (A) Representative family of traces of T-Type Ca²⁺ currents from DRG sensory treated acutely (<10 min) with vehicle (0.01% DMSO) or 5bk (20 μM). Voltage protocol used to evoke the currents is shown. (B) Summary of the normalized (pA/pF) T-Type calcium current density versus voltage relationship and (C) peak T-Type Ca²⁺ current density at −10 mV (mean±SEM) from DRG sensory neurons treated as indicated. (D) Boltzmann fits for normalized conductance G/G_(max) voltage relations for voltage dependent activation of T-type currents. (E) Time-dependent activation (10-90% rise time) from I-V curves and at −40mV (F) in DRG cells shown calculated from the data in B. (G) Boltzmann fits for normalized conductance G/G_(max) voltage relations for voltage dependent inactivation of sensory neurons treated as indicated. (H) Deactivating tail currents in DRG neurons treated acutely with vehicle (0.01% DMSO) or 5bk (20 μM) were fit with a single-exponential function. The resulting τ values are plotted. (I) Recovery from inactivation in indicated groups. Data are averaged and fitted by double exponential association (p values as indicated, Mann-Whitney test). All graphs show mean±s.e.m. with individual data points showed when possible.

FIG. 5A-K: 5bk inhibits T-Type Ca2+ currents in dorsal root ganglion (DRG) sensory neurons. (A) Representative family of traces of T-Type Ca2+ currents from DRG sensory treated overnight with vehicle (0.01% DMSO) or 5bk (20 μM). Voltage protocol used to evoke the currents is shown. (B) Summary of the normalized (pA/pF) T-Type calcium current density versus voltage relationship and (C) peak T-Type Ca²⁺ current density at −10 mV (mean±SEM) from DRG sensory neurons treated as indicated. (D) Boltzmann fits for normalized conductance G/G_(max) voltage relations for voltage dependent activation of T-type currents. (E) Inactivation τ, which is calculated from a single-exponential fit of the decaying portion of the current waveforms using a single-exponential equation: y=A₁×e^((−x/) ⁹⁶ ^(l))+y₀, where A₁ is the amplitude, τ₁ is the decay constant, and y₀ is the offset. (F) This analysis was also isolated at −40 mV. (G) Time-dependent activation (10-90% rise time) from I-V curves and at −40 mV (H) in DRG cells shown calculated from the data in B. (I) Boltzmann fits for normalized conductance G/G_(max) voltage relations for voltage dependent inactivation of sensory neurons treated as indicated. (J) Deactivating tail currents in DRG neurons treated with vehicle (0.01% DMSO) or 5bk (20 μM) were fit with a single-exponential function. The resulting τ values are plotted. (K) Recovery from inactivation in indicated groups. Data are averaged and fitted by double exponential association (n=16-19 cells per condition). All graphs show mean±s.e.m. with individual data points showed when possible. P values of comparisons between treatments are as indicated; see statistical analysis described in Table 1.

FIG. 6A-T: 5bk does not inhibit high voltage-activated Ca²⁺ currents in dorsal root ganglion (DRG) sensory neurons. (A, F, K, P) Pharmacological isolation was achieved by the indicated cocktail of toxins/small molecules. The voltage protocol used to elicit the currents is also shown. (B, G, I, Q) Representative traces of DRG neurons treated overnight with 0.1% DMSO (control) or 20 μM 5bk. (C, H, M, R) Summary of the normalized (pA/pF) HVA calcium current density versus voltage relationship and (D, I, N, S) peak HVA Ca²⁺ current density at +20 mV (mean±SEM) from DRG sensory neurons treated as indicated. Boltzmann fits for normalized conductance G/G_(max) voltage relations for voltage dependent activation and inactivation (E, J, O, T) of sensory neurons treated as indicated. Voltage dependent activation was assessed with the protocol shown in (E). The V_(0.5) and slope (k) values for activation and inactivation are presented in FIG. 7 . P values of comparisons between treatments are as indicated; see statistical analysis described in Table 1.

FIG. 7A-D: Boltzmann fits for normalized conductance G/G_(max) voltage relations for voltage dependent activation and inactivation (data shown in FIG. 6 ) of the sensory neurons treated overnight as indicated with 0.01% DMSO or 5bk. Half-maximal activation and inactivation (V_(1/2)) and slope values (k) for activation and inactivation for the various HVA subtypes of calcium channels.

FIG. 8A-E: 5bk does not affect Na⁺ currents in dorsal root ganglion (DRG) neurons. (A) Representative traces of Na⁺ currents from DRG sensory neurons treated overnight with 0.1% DMSO (control) or 20 μM 5bk. Currents were evoked by 150 ms pulse between −70 and +60 mV. Summary of the normalized (pA/pF) sodium (B) current density versus voltage relationship and (C) peak Na⁺ current density at −10 mV (mean±SEM) from DRG neurons treated as indicated. (D) Boltzmann fits for normalized conductance G/G_(max) voltage relations for voltage dependent activation and inactivation of sensory neurons treated as indicated. V_(1/2) values for activation and inactivation are indicated and were not significantly different between the treatment conditions (P>0.05, Mann-Whitney test). (E) Summary of the peak TTX-sensitive (F) Na⁺ current density (mean±SEM) from DRG neurons treated as indicated. (p value as indicated, Mann-Whitney test). TTX-sensitive and TTX-resistant fractions were calculated as described in the Methods section.

FIG. 9 : Downregulation of CaV3.2 blocks 5bk-mediated inhibition of depolarization-evoked Ca₂ influx through T-type Ca₂₊ channels. Dorsal root ganglion neurons were transfected during plating with a GFP construct and a scramble siRNA or with siRNAs against CaV3.1, CaV3.2 or CaV3.3. The bar graph shows normalized peak calcium response averages±S.E.M. of DRG sensory neurons treated as indicated. Responses were normalized to that of DMSO (vehicle) in the siRNA scramble condition. Representative time courses of the change in 340 nm/380 nm ratio for the response of representative neurons imaged in a preparation treated with 0.01% DMSO or 5bk are shown above the bar graphs. These experiments were done in a blinded fashion. P values of comparisons between treatments (n=10-42 cells per condition) are as indicated; see statistical analysis described in Table 1.

FIG. 10A-I: Constellation pharmacology-based characterization of neuronal populations in DRG sensory neurons treated with 5bk. (A) Representative traces of sensory neurons treated overnight with 0.01% DMSO (vehicle) or (B) 20 μM concentration of 5bk responding to constellation pharmacology triggers (menthol (400 nM), histamine (50 μM), ATP (10 μM), AITC (200 μM), acetylcholine (1 mM), capsaicin (100 nM) and KCl (90 mM)) during Ca²⁺ imaging. Each trace represents an individual neuron; a typical experimental trial records the responses of >300 neurons concurrently. (C) Number of overall functional DRG sensory neuronal classes as a result of treatment with DMSO or 5bk (20 μM). (D) Percentage of DRG sensory neurons that responded to indicated number of triggers. (E) Percentage of sensory neurons responding to major classes and (F) indicated subclasses of constellation triggers. (G) Average peak Ca²⁺ response post-indicated treatment for DRG neurons following stimulation by major classes of constellation triggers. (H) Area under the curve is shown for calcium response in sensory neurons post-indicated treatment, after stimulation by major classes of constellation triggers. Area under the curve was calculated with Graphpad Prism software using the trapezoid rule. (I) Average peak KCl-evoked response of sensory neurons post-indicated treatment. P values of comparisons between treatments are as indicated; see statistical analysis described in Table 1. Abbreviations for constellation triggers are as follows: ACh=acetylcholine; AITC=allyl isothiocyanate; ATP=adenosine triphosphate; Hist=histamine; Ment=menthol; Cap=capsaicin; KCl=potassium chloride. Data was collected from a total of 5 independent experiments with an overall sample of 2002 for control conditions and 2902 for 5bk (20 μM).

FIG. 11 : Representative images of vehicle-treated DRG neurons post-challenge with constellation pharmacology triggers. Differential interference contrast (DIC) and pseudocolored fluorescent images of DRG neurons treated with vehicle, visualized for Fura2-AM before and after stimulations with each of the constellation triggers: menthol (400 nM), histamine (50 μM), ATP (10 μM), AITC (200 μM), acetylcholine (1 mM), capsaicin (100 nM) and KCl (90 mM)) during Ca²⁺ imaging. Scale bar is 50 μm. Size heat map reports number of DRG neurons of indicated size (measured by neuronal area) responding to constellation triggers.

FIG. 12 : Representative images of 5bk-treated DRG neurons post-challenge with constellation pharmacology triggers. Differential interference contrast (DIC) and pseudocolored fluorescent images of DRG neurons treated with 5bk (20 μM), visualized for Fura2-AM before and after stimulations with each of the constellation triggers: menthol (400 nM), histamine (50 μM), ATP (10 μM), AITC (200 μM), acetylcholine (1 mM), capsaicin (100 nM) and KCl (90 mM)) during Ca²⁺ imaging. Scale bar is 50 μm. Size heat map reports number of DRG neurons of indicated size (measured by neuronal area) responding to constellation triggers.

FIG. 13A-C: 5bk does not bind to the opioid receptors. Competition radioligand binding was performed in CHO cells expressing the human mu/delta/kappa opioid receptors (MOR, DOR, or KOR, respectively) (see Methods for details). 5bk or a positive control compound was competed against ³H-diprenorphine in all 3 cell lines. Curves reported as the mean±SEM of the mean value from each individual experiment in n=3 independent experiments. The Ki also reported as the mean±SEM of the individual value from each of n=3 independent experiments. 5bk did not produce competition binding up to 10 μM in any cell line. (A) MOR: Naloxone Ki=43.3±1.9 nM. (B) DOR: Naloxone Ki=48.1±9.1 nM. (C) KOR: U50,488 Ki=12.7±0.6 nM.

See statistical analysis described in Table 1.

FIG. 14A-C: 5bk decreases spontaneous excitatory synaptic transmission in substantia gelatinosa neurons. (A) Representative traces recorded from control (0.1% DMSO) and 5bk (25 μM)-treated groups. (B) Spontaneous excitatory post synaptic current (EPSC) amplitudes as a result of treatment with DMSO or 5bk. (C) Spontaneous EPSC frequency as a result of treatment with DMSO or 5bk. P values of comparisons between treatments (n=17-18 per condition) are as indicated; see statistical analysis described in Table 1.

FIG. 15 : 5 bk decreases evoked CGRP release. Spinal cords from adult rats (n=4 per condition) were used to assess potassium chloride (KCl, 90 mM)-induced calcitonin gene related peptide (CGRP) release from nerve terminals. KCl increased CGRP release in control rat spinal cords, which was significantly higher than in cords from 5bk-treated rats (*p<0.05 vs. control; two-way ANOVA post hoc Sidak's test). P values of comparisons between treatments are as indicated; see statistical analysis described in Table 1.

FIG. 16A-I: GP120, paclitaxel, and spinal nerve ligation induced nociceptive behaviors are reduced upon treatment with 5bk. (A) Rats received spinal nerve ligation (SNL) injury with allodynia measurement on the left hind paw. Paw withdrawal thresholds were significantly decreased 7 days after surgery. 5bk (2 μg/5 μL) or vehicle (saline) were injected into the intrathecal space and PWTs measured. Paw withdrawal thresholds were significantly reversed at the indicated times after injection of 5bk (n=6; *p<0.05; two-way ANOVA with a Student-Neuman-Kuels post hoc test). (B) Data from D are transformed and presented as mean±s.e.m. percentage of maximal anti-allodynia (see Methods). (C) Area under the curve (AUC), using the trapezoid method, for PWT. Statistical significance is indicated by asterisks (*p<0.05, one-way analysis of variance with Tukey's post hoc analysis) in comparison to vehicle-treated rats. (D) Paw withdrawal threshold (PWTs) of adult rats (n=7) was measured 15 days after 3 intrathecal injections of glycoprotein-120. Rats were treated with saline (vehicle) or 5bk (2 μg/5 μL, intrathecal) as indicated. Asterisks indicate statistical significance compared with animals treated with saline (*p<0.05; 2-way ANOVA with a Dunnet's hoc test). (E) Data from A are transformed and presented as mean±s.e.m. percentage of maximal anti-allodynia (see Methods). (F) Area under the curve was derived as indicated before using Graphpad prism. Statistical significance is indicated by asterisks (*p<0.05, Mann-Whitney) in comparison to vehicle-treated rats. (G) Paw withdrawal threshold of adult rats (n=7) was measured 15 days after 4 intraperitoneal injections of paclitaxel. Rats were treated with saline (vehicle) or 5bk (2 μg/5 μL, intrathecal) as indicated. Data from G are transformed and presented as mean±s.e.m. percentage of maximal anti-allodynia (see Methods). Asterisks indicate statistical significance compared with tissue treated with saline (*p<0.05; 2-way ANOVA with a Dunnet's post hoc test). (I) Area under the curve was derived again as indicated before using Graphpad prism. Statistical significance is indicated by asterisks (*p<0.05, Mann-Whitney) in comparison to vehicle-treated rats. Exact p values of comparisons between treatments are described in Table 1.

FIG. 17A-B: Treatment with 5bk does not induce motor deficits or alter anxiety levels. (A) Rats (n=6) were subjected to the rotarod performance test as previously described in the Methods in order to test for motor deficits. Vehicle and 5bk-treated animals remained on the rotarod for an average of 172±7.3 and 170±9.6 seconds (cutoff 180 seconds), respectively, when tested over the course of 300 minutes. No significant motor deficits were noted in comparison to vehicle-treated animals. (B) Rats (n=7) were subjected to the elevated plus maze (EPM) test as detailed (see methods); the anxiety index, integrates measurement of times and entries of the animals into the open and closed arms of the EPM, and is shown both pre- and post (1 hour) injection of either 0.01% DMSO (vehicle) or 5bk (2 μg/5 μL, intrathecal) as indicated. See statistical analysis described in Table 1.

FIG. 18A-C: Docking of 5bk and Z944 on the Cav3.2 structure. (A) Ribbon diagram of CaV3.2 channel modeled on the CaV3.1 cryoEM structure (PDB ID 6kzp [94]) using Phyre2 [39]. Aligned inhibitor Z944 from CaV3.1 structure shown in gray and docked 5bk in green sticks representation. (B) Surface representation of ligand binding pocket showing overlap of the Z944 binding mode and 5bk docked pose. (C) Interactions within 4 A of 5bk with polar and nearest ring contacts indicated by dashes. 5bk was prepared with LigPrep and docked with Glide (Schrödinger Release 2019-4) [24] in Xtra Precision mode (docking score: −6.7).

FIG. 19A-B: (A) 2-D similarity of 5bk (left) and Z944 (right) with common pharmacophore features color-coded in red and blue, respectively. (B) 3-D overlay of energy-minimized conformers of 5bk and Z944.

FIG. 20A-D: hERG channel was expressed in oocytes and the current was recorded with and without 100 μM of the indicated compounds. (A) Summary data of % hERG current remaining with the various compounds. E4031, a known hERG channel blocker, was used as a positive control (see, Vandenberg J I, et al., Physiol Rev 2012;92(3):1393-1478). Amantadine was used as a negative control. Representative traces from oocytes treated with vehicle (0.01% DMSO, black trace) or E4031 (B, red trace), Ama (C, red trace), or 5bk (D, red trace).

DETAILED DESCRIPTION OF THE INVENTION

The voltage-gated calcium (CaV3.1-3.3) channels constitute the T-type subfamily, whose dysfunctions are associated with epilepsy, psychiatric disorders, and chronic pain. The unique properties of low voltage-activation, faster inactivation, and slower deactivation of these channels support their role in modulation of cellular excitability and low-threshold firing. Thus, selective T-type calcium channel antagonists are highly sought after.

Experiments conducted during the course of developing embodiments for the prestn invention explored Ugi-azide multicomponent reaction (MCR) products to identify a selective antagonist of the T-type calcium channel. Of the 46 compounds tested, an analog of benzimidazolonepiperidine—5bk (1-{1-[(R)-{1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl}(thiophen-3-yl)methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one), inhibited depolarization-induced calcium influx in rat sensory neurons. Blockage of T-type calcium channels by 5bk was further confirmed in wholecell patch clamp assays in dorsal root ganglion (DRG) neurons, where pharmacological isolation of T-type currents led to a concentration-dependent inhibition with a low micromolar IC₅₀. Genetic knockdown revealed CaV3.2 to be the isoform inhibited by 5bk. 5bk inhibited spontaneous excitatory post synaptic currents and depolarization-evoked release of calcitonin gene-related peptide (CGRP) from lumbar spinal cord slices. Notably, 5bk did not target human mu, delta, or kappa opioid receptors. 5bk reversed mechanical allodynia in rat models of HIV-associated peripheral sensory neuropathy and chemotherapy-induced peripheral neuropathy (CIPN) and spinal nerve ligation (SNL) induced neuropathy, without effects on locomotor activity or anxiety.

Thus, 5bk represents a novel compound in the fight to develop non-addictive pain therapeutics.

As such, the present invention addresses the need for effective therapies for pain related to CaV3.2 activity by providing potent and selective CaV3.2 inhibitors.

Accordingly, this invention relates to a new class of small-molecules having a piperazine or piperidine structure which function as inhibitors of the CaV3.2 voltage gated calcium channel activity (e.g., depolarization-induced calcium influx), and their use as therapeutics for the treatment and/or prevention of CaV3.2 related pain (e.g., HIV-associated peripheral sensory neuropathy, chemotherapy-induced peripheral neuropathy (CIPN), spinal nerve ligation (SNL) induced neuropathy) and related conditions.

In a particular embodiment, compounds encompassed within Formula I are provided:

including pharmaceutically acceptable salts, solvates, and/or prodrugs thereof.

Formula I is not limited to a particular chemical moiety for X, R1, R2, and R3. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit CaV3.2 voltage gated calcium channel activity. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit depolarization-induced calcium influx related to CaV3.2 voltage gated calcium channel activity. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit, prevent and/or ameliorate neuropathy pain related to CaV3.2 activity. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit, prevent and/or ameliorate pain related to CaV3.2 activity. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit, prevent and/or ameliorate pain related to HIV-associated peripheral sensory neuropathy. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit, prevent and/or ameliorate pain related to chemotherapy-induced peripheral neuropathy (CIPN). In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit, prevent and/or ameliorate pain related to spinal nerve ligation (SNL) induced neuropathy. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit spontaneous excitatory post-synaptic currents via actions presynaptically. In some embodiments, the particular chemical moiety for X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit release of the pronociceptive neurotransmitter calcitonin gene related peptide (CGRP).

In some embodiments, X is C thereby rendering the compound a piperidine based compound.

In some embodiments, X is N thereby rendering the compound a piperazine based compound.

In some embodiments, R1 is selected from

In some embodiments, R1 is hydrogen.

In some embodiments, R2 is selected from

In some embodiments, R2 is hydrogen.

In some embodiments, R3 is selected from

In some embodiments, R3 is hydrogen.

In some embodiments, the compound is recited in FIG. 1B.

The invention further provides processes for preparing any of the compounds of the present invention.

In some embodiments, the compositions and methods of the present invention are used to treat diseased cells, tissues, organs, or pathological conditions and/or disease states in an animal (e.g., a mammalian patient including, but not limited to, humans and veterinary animals). In this regard, various diseases and pathologies are amenable to treatment or prophylaxis using the present methods and compositions. A non-limiting exemplary list of these diseases and conditions includes, but is not limited to, conditions related to aberrant CaV3.2 activity, pain related to CaV3.2 voltage gated calcium channel activity, pain related to HIV-associated peripheral sensory neuropathy, pain related to chemotherapy-induced peripheral neuropathy (CIPN); pain related to spinal nerve ligation (SNL) induced neuropathy, neuropathy related to CaV3.2 activity, and diabetic neuropathy related to CaV3.2 activity.

Some embodiments of the present invention provide methods for administering an effective amount of a compound of the invention and at least one additional therapeutic agent (including, but not limited to, any agent useful in treating pain related to CaV3.2 activity).

Compositions within the scope of this invention include all compositions wherein the compounds of the present invention are contained in an amount which is effective to achieve its intended purpose. While individual needs vary, determination of optimal ranges of effective amounts of each component is within the skill of the art. Typically, the compounds may be administered to mammals, e.g. humans, orally at a dose of 0.0025 to 50 mg/kg, or an equivalent amount of the pharmaceutically acceptable salt thereof, per day of the body weight of the mammal being treated for disorders responsive to induction of apoptosis. In one embodiment, about 0.01 to about 25 mg/kg is orally administered to treat, ameliorate, or prevent such disorders. For intramuscular injection, the dose is generally about one-half of the oral dose. For example, a suitable intramuscular dose would be about 0.0025 to about 25 mg/kg, or from about 0.01 to about 5 mg/kg.

The unit oral dose may comprise from about 0.01 to about 1000 mg, for example, about 0.1 to about 100 mg of the compound. The unit dose may be administered one or more times daily as one or more tablets or capsules each containing from about 0.1 to about 10 mg, conveniently about 0.25 to 50 mg of the compound or its solvates.

In a topical formulation, the compound may be present at a concentration of about 0.01 to 100 mg per gram of carrier. In a one embodiment, the compound is present at a concentration of about 0.07-1.0 mg/ml, for example, about 0.1-0.5 mg/ml, and in one embodiment, about 0.4 mg/ml.

In addition to administering the compound as a raw chemical, the compounds of the invention may be administered as part of a pharmaceutical preparation containing suitable pharmaceutically acceptable carriers comprising excipients and auxiliaries which facilitate processing of the compounds into preparations which can be used pharmaceutically. The preparations, particularly those preparations which can be administered orally or topically and which can be used for one type of administration, such as tablets, dragees, slow release lozenges and capsules, mouth rinses and mouth washes, gels, liquid suspensions, hair rinses, hair gels, shampoos and also preparations which can be administered rectally, such as suppositories, as well as suitable solutions for administration by intravenous infusion, injection, topically or orally, contain from about 0.01 to 99 percent, in one embodiment from about 0.25 to 75 percent of active compound(s), together with the excipient.

The pharmaceutical compositions of the invention may be administered to any patient which may experience the beneficial effects of the compounds of the invention. Foremost among such patients are mammals, e.g., humans, although the invention is not intended to be so limited. Other patients include veterinary animals (cows, sheep, pigs, horses, dogs, cats and the like).

The compounds and pharmaceutical compositions thereof may be administered by any means that achieve their intended purpose. For example, administration may be by parenteral, subcutaneous, intravenous, intramuscular, intraperitoneal, transdermal, buccal, intrathecal, intracranial, intranasal or topical routes. Alternatively, or concurrently, administration may be by the oral route. The dosage administered will be dependent upon the age, health, and weight of the recipient, kind of concurrent treatment, if any, frequency of treatment, and the nature of the effect desired.

The pharmaceutical preparations of the present invention are manufactured in a manner which is itself known, for example, by means of conventional mixing, granulating, dragee-making, dissolving, or lyophilizing processes. Thus, pharmaceutical preparations for oral use can be obtained by combining the active compounds with solid excipients, optionally grinding the resulting mixture and processing the mixture of granules, after adding suitable auxiliaries, if desired or necessary, to obtain tablets or dragee cores.

Suitable excipients are, in particular, fillers such as saccharides, for example lactose or sucrose, mannitol or sorbitol, cellulose preparations and/or calcium phosphates, for example tricalcium phosphate or calcium hydrogen phosphate, as well as binders such as starch paste, using, for example, maize starch, wheat starch, rice starch, potato starch, gelatin, tragacanth, methyl cellulose, hydroxypropylmethylcellulose, sodium carboxymethylcellulose, and/or polyvinyl pyrrolidone. If desired, disintegrating agents may be added such as the above-mentioned starches and also carboxymethyl-starch, cross-linked polyvinyl pyrrolidone, agar, or alginic acid or a salt thereof, such as sodium alginate. Auxiliaries are, above all, flow-regulating agents and lubricants, for example, silica, talc, stearic acid or salts thereof, such as magnesium stearate or calcium stearate, and/or polyethylene glycol. Dragee cores are provided with suitable coatings which, if desired, are resistant to gastric juices. For this purpose, concentrated saccharide solutions may be used, which may optionally contain gum arabic, talc, polyvinyl pyrrolidone, polyethylene glycol and/or titanium dioxide, lacquer solutions and suitable organic solvents or solvent mixtures. In order to produce coatings resistant to gastric juices, solutions of suitable cellulose preparations such as acetylcellulose phthalate or hydroxypropylmethyl-cellulose phthalate, are used. Dye stuffs or pigments may be added to the tablets or dragee coatings, for example, for identification or in order to characterize combinations of active compound doses.

Other pharmaceutical preparations which can be used orally include push-fit capsules made of gelatin, as well as soft, sealed capsules made of gelatin and a plasticizer such as glycerol or sorbitol. The push-fit capsules can contain the active compounds in the form of granules which may be mixed with fillers such as lactose, binders such as starches, and/or lubricants such as talc or magnesium stearate and, optionally, stabilizers. In soft capsules, the active compounds are in one embodiment dissolved or suspended in suitable liquids, such as fatty oils, or liquid paraffin. In addition, stabilizers may be added.

Possible pharmaceutical preparations which can be used rectally include, for example, suppositories, which consist of a combination of one or more of the active compounds with a suppository base. Suitable suppository bases are, for example, natural or synthetic triglycerides, or paraffin hydrocarbons. In addition, it is also possible to use gelatin rectal capsules which consist of a combination of the active compounds with a base. Possible base materials include, for example, liquid triglycerides, polyethylene glycols, or paraffin hydrocarbons.

Suitable formulations for parenteral administration include aqueous solutions of the active compounds in water-soluble form, for example, water-soluble salts and alkaline solutions. In addition, suspensions of the active compounds as appropriate oily injection suspensions may be administered. Suitable lipophilic solvents or vehicles include fatty oils, for example, sesame oil, or synthetic fatty acid esters, for example, ethyl oleate or triglycerides or polyethylene glycol-400. Aqueous injection suspensions may contain substances which increase the viscosity of the suspension include, for example, sodium carboxymethyl cellulose, sorbitol, and/or dextran. Optionally, the suspension may also contain stabilizers.

The topical compositions of this invention are formulated in one embodiment as oils, creams, lotions, ointments and the like by choice of appropriate carriers. Suitable carriers include vegetable or mineral oils, white petrolatum (white soft paraffin), branched chain fats or oils, animal fats and high molecular weight alcohol (greater than C₁₂). The carriers may be those in which the active ingredient is soluble. Emulsifiers, stabilizers, humectants and antioxidants may also be included as well as agents imparting color or fragrance, if desired. Additionally, transdermal penetration enhancers can be employed in these topical formulations. Examples of such enhancers can be found in U.S. Pat. Nos. 3,989,816 and 4,444,762; each herein incorporated by reference in its entirety.

Ointments may be formulated by mixing a solution of the active ingredient in a vegetable oil such as almond oil with warm soft paraffin and allowing the mixture to cool. A typical example of such an ointment is one which includes about 30% almond oil and about 70% white soft paraffin by weight. Lotions may be conveniently prepared by dissolving the active ingredient, in a suitable high molecular weight alcohol such as propylene glycol or polyethylene glycol.

One of ordinary skill in the art will readily recognize that the foregoing represents merely a detailed description of certain preferred embodiments of the present invention. Various modifications and alterations of the compositions and methods described above can readily be achieved using expertise available in the art and are within the scope of the invention.

EXAMPLES

The following examples are illustrative, but not limiting, of the compounds, compositions, and methods of the present invention. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in clinical therapy and which are obvious to those skilled in the art are within the spirit and scope of the invention.

The following abbreviations are relevant for the following examples: A549, adenocarcinomic human alveolar basal epithelial cells, AITC, Allyl isothiocyanate; CaV3, voltage-gated calcium channel subfamily 3; CC50, cytotoxic concentration; CGRP, calcitonin gene-related peptide; CHO, Chinese Hamster Ovary; CIPN, chemotherapy-induced peripheral neuropathy; DOR, delta opioid receptor DRG, dorsal root ganglia; EPM, elevated plus maze; hERG, human Ether-a-go-go-Related gene, codes for Kv11.1 channel; HIV gp120 , human immunodeficiency virus envelope glycoprotein; KOR, kappa opioid receptor; KCl, potassium chloride; LVA, low voltage-activated; MOR, mu opioid receptor; MCR, multicomponent reactions; MDCK, Madin-Darby Canine Kidney cells; sEPSCs, spontaneous excitatory post-synaptic currents; HVA, high-voltage-activated; IB4, isolectin B4; CCI, chronic constriction injury; SNI, spared nerve injury, PSNL, partial sciatic nerve ligation; 5bk, 1-{1-[(R)-{1-[(1S)-1-phenylethyl]-1,2,3,4-tetrazol-5-yl}(thiophen-3-yl)methyl]piperidin-4-yl}-3H-1,3-benzodiazol-2-one; Z944, {N}-[[1-[2-(˜{tert}-butylamino)-2-oxidanylidene-ethyl]piperidin-4-yl]methyl]-3-chloranyl-5-fluoranyl-benzamide.

Example I Chemical Synthesis

All compounds were synthesized using the Ugi-azide four-component reaction methodology as shown in FIG. 1A. Chemical structures for the compounds tested in the Ca₂₊ flux assay are shown in FIG. 1B. Inspection of the chemical structure of 5bk (FIG. 3 ) did not reveal any significant metabolic and toxic liabilities, [72] as similar structural components from 5bk are also found in a number of FDA-approved oral drugs (FIG. 2 ).

5bk was not cytotoxic to either Madin-Darby Canine Kidney (MDCK) cells or adenocarcinomic human alveolar basal epithelial (A549) cells (cytotoxic concentration, CC₅₀>100 μM).

Identification of Antagonists of Low Voltage Activated (LVA) T-Type Calcium Channels.

Using Fura 2-AM based ratiometric calcium-imaging assay as we have established before [23; 53; 54; 88], we screened an in-house diversity library of compounds (at 20 μM) for their inhibition of Ca2+ influx via low (triggered with 40 mM KCl) and high (triggered with 90 mM KCl) voltage activated calcium channels in primary rat dorsal root ganglion (DRG) neurons. The goal was to identify hits that inhibit LVA calcium channels but not high-voltage activated calcium channels. In the first set, one compound, 5aa, inhibited ˜45% of the Ca²⁺ influx when DRGs were depolarized with 40 mM KCl and ˜60% when depolarized with 90 mM KCl (FIG. 3A, B). As no compound in the initial round was selective for low voltage-activated calcium channels, we selected 5aa for further optimization with the primary goal of achieving preferential activity towards LVA channels.

Encouraged by discovery of this initial hit, we subsequently synthesized a focused library of 45 analogs of 5aa by varying the amine, aldehyde, and isocyanide components using the established Ugi-azide four-component reaction condition. The structures of the compounds are shown in FIG. 1B. Compounds 5ab, 5ak, 5al, 5ao, 5aq, 5at, 5aw, 5ax, 5ay, 5ba, 5be, 5bh, 5bi, 5bp, 5bq, 5br, 5bs, and 5bt were synthesized and tested as a diastereomer mixtures. Compounds 5bk and 5bl were tested as pure diastereomers and their absolute stereochemistry were confirmed by X-ray crystallography [93]. Three of the 46 compounds, 5ay 5bk, and 5bt inhibited>75% of Ca²⁺ influx when DRGs were depolarized with 40 mM KCl, of which 2 of these compounds 5ay and 5bt showed>50% inhibition when also triggered with 90 mM KCl (FIG. 3A, B). One compound, 5bk (FIG. 3C) appeared selective in inhibiting KCl-evoked Ca²⁺ influx with 88.5±2.6% inhibition (n=78) relative to the negative control (0.01% DMSO) when stimulated with 40 mM KCl and an ˜33.9±4.0% inhibition (n=78) of evoked Ca²⁺ influx when stimulated with 90 mM KCl. The inhibition was observed only after at least 30 minutes of application of 5bk and achieved a maximum with overnight treatment (FIG. 3D). The corresponding diastereomer, 5bl, did not show significant inhibition of Ca²⁺ flux with <25% signal reduction when DRGs were depolarized with either 40 mM or 90 mM KCl. Notably, compounds 5bk and 5bl were previously tested for their inhibition of the influenza virus polymerase PA-PB1 protein-protein interactions, and only compound 5bl was found to be active [93]. These results suggest compound 5bk interacts with T-type Ca²⁺ channels in a stereospecific manner. Overall, compound 5bk is the most potent and selective antagonist against the T-type Ca²⁺ channel among all the compounds tested.

We further analyzed the features of 5bk antagonism, finding a concentration-dependent inhibition of LVA currents with an IC₅₀ of 4.2±0.6 μM (FIG. 3E). The inhibition was time-dependent with increasing block observed with longer incubation periods (FIG. 3D). 5bk also did not inhibit hERG channel at 100 μM in two-electrode voltage clamp assay, which has important implications for therapeutic safety (SUPP*3).

5bk Inhibits T-type Ca2+ Channels in Sensory Neurons

One of the most potent hit compounds from the primary calcium imaging screening was 5bk (FIG. 3 ), which showed nearly ˜90% inhibition of Ca2+ channel influx at 20 μM when DRGs were depolarized with 40 mM KCl. As the inhibition of calcium influx elicited by 5bk appeared to be more pronounced with 40 mM KCl versus 90 mM KCl (FIG. 3 ), we chose to test if T-type calcium channels were being preferentially targeted by this compound. In DRG sensory neurons, the a subunits of Cav3.2 and Cav3.3 represent the majority of T-type Ca2+ channels [92]. Therefore, we used electrophysiology protocols described before [14] to record T-type currents. From a holding potential of −90 mV, we used 200-ms depolarization steps to change the membrane potential from −70 to +60 mV (10 mV increments) to evoke prototypical T-type calcium currents (FIG. 5A). After treatment with 0.01% DMSO (vehicle, n=16) or 5bk (20 μM, n=16), we recorded low voltage-activated calcium currents (FIG. 5A) from DRG neurons with an average diameter between 20-30 μm. We measured current voltage (I-V) relationships (FIG. 5B) and observed that treatment with 5bk reduced T-type calcium current amplitudes between −20 mV and +10 mV test potentials (FIG. 5B). At peak current density (−10 mV), there was ˜42.2% reduction in current in 5bk-treated cells compared with vehicle-treated controls (FIG. 5C). Treatment with 5bk did not alter the channel gating properties as we measured a similar half-maximal activation (V0.5) of T-type calcium channels in both conditions (FIG. 5D). The kinetics of macroscopic current inactivation (FIG. 5E) were unchanged at all membrane potentials tested (−40 mV, FIG. 5F). The time-dependent activation (10 to 90% rise time) of T-type currents was not affected by treatment with 5bk (FIG. 5G-H). We next tested whether 5bk could control the voltage-dependent kinetics of channel inactivation (FIG. 5I) and found this property to also not be affected by treatment with 5bk. Deactivating tail currents calculated using the single exponential function: y=A1×e(−x/τ1)+y0, where A1 is the amplitude, τ1 is the decay constant, and y0 is the offset. The resulting τ values (FIG. 5J), showed no differences irrespective of the treatment condition. Finally, because upon long membrane hyperpolarizations in DRG neurons T-type calcium channels can recover from inactivation, we tested if this biophysical parameter could be affected by treatment with 5bk. This property has important consequences on the firing properties of sensory neurons expressing T-type calcium channels. Thus, we tested the recovery from inactivation using a double pulse protocol with a variable interpulse duration at −90 mV (FIG. 5K) after a 500-ms-long inactivating pulse (Vh=−90 mV; Vt=−30 mV). T-type currents recovered fully, independently of the treatment condition (FIG. 5K). Taken together, our results show that 5bk specifically blocks T-type calcium channels in DRG neurons.

Given the lack of effect of 5bk on the kinetic and voltage-dependent properties of T-type calcium currents, it is possible that 5bk downregulates functional T-type channels by acting on second messenger pathways. To test this possibility, we applied 5bk acutely during recordings. The results (FIG. 4 ), showed no inhibition of T-type currents, consistent with our data obtained from calcium imaging (FIG. 3D). Consequently, biophysical properties (i.e. voltage-activation, inactivation, recovery from inactivation) of these LVA channels were also unaffected by 5bk (FIG. 4 ).

To further explore selectivity of 5bk for Cav3 over other HVA channel types, we examined how other channels were affected by 5bk (FIG. 6 ). 5 bk, applied overnight, had no effect on pharmacologically isolated L-type (CaV1.x) (FIG. 6C, D), P/Q-type (CaV2.1) (FIG. 6H, I), N-type (CaV2.2) (FIG. 6M, N), or R-type (CaV2.3) (FIG. 6R, S) nor did it affect the V_(1/2) of activation or inactivation (FIG. 6E, J, O, T and FIG. 7 ). Finally, we also observed no effects of 5bk on tetrodotoxin-sensitive or -resistant voltage-gated sodium currents (FIG. 8 ).

5bk inhibits CaV3.2 T-Type Ca2+ Channels

To test if 5bk preferentially targets a specific T-type Ca2+ channel subunit we used a knockdown strategy (using short interfering RNA (siRNA)) to eliminate either CaV3.1, CaV3.2 or CaV3.3 in DRG sensory neurons (FIG. 9 ). DRG neurons were electroporated with the indicated siRNA (or a scrambled negative control) in combination with a GFP expressing plasmid (to identify transfected cells). The cells were cultured for 24 hours before adding 20μM of 5bk overnight (or 0.1% DMSO as control) and then tested using 40 mM KCl as a trigger (FIG. 9 ). In scramble siRNA-transfected cells, 5bk inhibited 40 mM KCl evoked Ca2+ influx by ˜53% (FIG. 9 ). In neurons with a knock down of CaV3.2, 5bk failed to inhibit the 40 mM KCl evoked Ca2+ influx. In contrast, after the knockdown of either CaV3.1 or CaV3.3, significant inhibition of calcium influx was still noted upon depolarization with 40 mM KCl (FIG. 9 ). Thus, we conclude that 5bk may preferentially inhibits CaV3.2 Ca2+ channel subunits. A limitation of this approach is that the low expression of CaV3.1 or CaV3.3 in native DRG neurons may mask a potential inhibitory action of 5bk.

5bk's Effects on Subpopulations of DRG Neurons

The data presented thus far demonstrates the potential for 5bk to inhibit Ca2+ influx via T-type Ca2+ channel. However, which cell-specific neuronal classes are implicated in 5bk's mechanism of action has not yet been addressed. In order to investigate this, we used the previously described constellation pharmacology protocol[75; 76] to explore cell-specific functionality as a result of key signaling proteins that define precise cell types. The constellation pharmacology assay poses 6 consecutive challenges, each 6 minutes apart, to compare Ca2+ influx due to activity of Ca2+-associated membrane proteins: Ca2+ permeable ligand-gated ion channels, metabotropic receptors and voltage-gated Ca2+ channels. Following these 6 stimulations, KCl-evoked response due to membrane depolarization is used to assess viability of neurons; neurons not responsive to KCl are excluded from analysis.

The versatility in neuronal responsivity is demonstrated by exemplary traces of rat DRG sensory neurons treated with control (0.1% DMSO) or a 20 μM concentration of 5bk as specified (FIGS. 10A, B). Representative images of DMSO and 5bk-treated neurons (FIG. 11 , FIG. 12 ), show examples of calcium responses before and after challenge with each of the constellation triggers: menthol (400 nM), histamine (50 μM), ATP (10 μM), AITC (200 μM), acetylcholine (1 mM), capsaicin (100 nM) and KCl (90 mM)) during the constellation pharmacology protocol. Inhibition of Ca2+ influx due to KCl stimulus was again inhibited as a result of treatment with 5bk; this is consistent with our previous data (FIG. 3 ). Sensory neurons were incubated overnight with the specified treatment, 0.01% DMSO (n=2002) or 5bk (n=2902) and imaged the following day with the constellation pharmacology protocol. Data was collected from 5 independent experiments, and individual neuronal responses to each constellation trigger were analyzed. Neurons with responses under 10% of baseline fluorescence were excluded from the analyses.

We began with exploring the effect of 5bk on the overall functionality of sensory neurons. This was analyzed in terms of functional cell subclasses present in the population of neurons treated with 5bk in comparison to the control population. Notably, more functional subclasses were present in the population of neurons treated with 5bk in comparison to those treated with vehicle control (FIG. 10C). However, response of neurons to the number of stimulatory challenges, independent of which specific agonists triggered response, was not altered by 5bk treatment (FIG. 10D). Furthermore, we inquired whether 5bk affected the sensitivity of DRGs to the different constellation triggers, by analyzing the percent of cells responding to a specific constellation trigger, independently of any other constellation triggers these neurons may have responded to: we noted an increased sensitivity to ATP stimulation and decreased sensitivity to capsaicin following treatment with 5bk (FIG. 10E). Similarly, following treatment with 5bk, there were more responders in functional cell subclasses including ATP as an agonist, and less responders in those including capsaicin as an agonist (FIG. 10F).

In a more targeted inquiry, we also investigated the effect of 5bk on the extent of Ca2+ influx following specific stimulation by each constellation trigger. Thus, we analyzed peak Ca2+ responses (FIG. 10G) and area under the curve (AUC) of these responses (FIG. 10H) in sensory neurons as a result of the specified treatment. Interestingly, while 5bk significantly altered peak Ca2+ responses to menthol, and capsaicin stimulation, only stimulation with capsaicin altered the AUC of Ca2+ response: the AUC was decreased.

We then asked if KCl-evoked Ca2+ response as a result of 5bk would be altered in a functional class specific manner (FIG. 10I). To test this, we assessed average peak Ca2+ response due to KCl challenge in sensory neurons that specifically responded to a particular constellation trigger, independent of any other constellation triggers that they might have responded to. Treatment with 5bk significantly decreased KCl-evoked Ca2+ response in sensory neurons that responded to an ATP and menthol stimulus; however, DRGs that responded to ACh, AITC, Histamine, and capsaicin did not have significantly altered KCl-evoked response due to 5bk treatment (FIG. 100 .

These results reveal the full actionable mechanisms of Ca2+ inhibition by 5bk and suggest its potential efficacy as an anti-nociceptive agent.

5bk Does Not Bind to the Orthosteric Site of the Opioid Receptors

To assess if 5bk could work by off-target binding to the opioid receptors, we performed competition radioligand binding at all 3 opioid receptors in vitro. We competed 5bk and a positive control compound (naloxone for MOR and DOR, U50,488 for KOR) vs. a fixed concentration of ³H-diprenorphine in Chinese Hamster Ovary (CHO) cells expressing the human μ (MOR), δ (DOR), or κ (KOR) opioid receptor. We found that 5bk did not bind to any opioid receptor up to a 10 Mm concentration (FIG. 13A-C). In contrast, the positive control compounds bound to all 3 targets with expected affinity (FIG. 13A-C). These results strongly suggest that 5bk is not engaging the opioid receptors, and that potential anti-nociception would thus not be as a result of opioid receptor association.

5bk Inhibits Spontaneous Excitatory Post-Synaptic Currents Via Presynaptic Actions

Since T-type calcium channels contribute to action potential firing and neurotransmitter release [10], we performed electrophysiological recordings in substantia gelatinosa neurons in the superficial layers (within laminae I-II) of the spinal dorsal horn to measure whether 5bk could inhibit spontaneous excitatory post-synaptic currents (sEPSCs). There was no significant decrease in spontaneous EPSC amplitude (post-synaptic effect) (FIG. 14A, B) of neurons treated with 0.1% DMSO or 5bk (20 μM). However, 5bk treatment decreased sEPSC frequency (DMSO, 1.96±0.21 Hz; 5bk, 1.26±0.17 Hz, P<0.05) (FIG. 14C), suggesting a presynaptic suppression of neurotransmitter release by 5bk.

5bk Inhibits Calcitonin Gene Related Peptide (CGRP) Release in Spinal Cord Slices

Calcium entry via T-type Ca2+ channels contributes to the release of neurotransmitters, including CGRP, in the spinal dorsal horn. [63; 71; 79] Emergent evidence overall suggests that CGRP facilitates nociceptive transmission and contributes to development and maintenance of a sensitized, hyper-responsive state not only of the primary afferent sensory neurons but also of second-order pain transmission neurons within the CNS. This CGRP activity is thus thought to contribute to central sensitization as well. CGRP concentrations in spinal cords was measured directly via ELISA kits as described by us previously. [7] We observed that 5bk inhibits KCl-evoked CGRP release from spinal cords, suggesting 5bk could be anti-nociceptive in vivo (FIG. 15 ).

Appraisal of 5bk in Three Models of Neuropathy in Rat

We used the spinal nerve ligation (SNL) model of neuropathic pain to evaluate the potential of 5bk to reverse nociception. SNL injury efficiently reduced paw withdrawal thresholds (PWTs) (mechanical allodynia, FIG. 16A) 7 days post injury. Spinal administration of 5bk significantly increased PWTs (FIG. 16A) for 2 hours during the course of the experiment. Transformation of the behavior data into percent anti-allodynia demonstrated a significant reversal of allodynia in rats injected with 5bk (FIG. 16B). AUC analysis confirmed the reversal of mechanical allodynia (FIG. 16C) compared to vehicle-treated injured animals.

Of the many complications associated with both HIV and chemotherapy, a common symptom is HIV induced sensory neuropathy and chemotherapy-induced peripheral neuropathy (CIPN) respectively [48]. Since voltage-gated Ca₂₊ channels have previously been found to contribute to neuropathic pain [57], we explored the potential utility of 5bk in reversing the nociceptive effects induced by injections of the HIV envelope glycoprotein (gp120) or the chemotherapeutic drug paclitaxel. To test this, we first induced mechanical allodynia via 3 intrathecal injections of gp120, which has been shown to induce mechanical allodynia in animals[51; 91]; a subsequent reversal of mechanical allodynia by intrathecal injection of 5bk (2 μg/5 μL) was seen at approximately 60 minutes post-gp120 injection and lasted for 4 hours (FIG. 16D). The same was true for the transformed data plotted as % anti-allodynia which was significantly reversed in rats injected with 5bk (FIG. 16E). This reversal of mechanical allodynia was also substantiated with a corresponding increase in area under the curve (FIG. 16F) associated with intrathecal administration of 5bk.

Next, we assessed the effectiveness of intrathecally injected 5bk (2 μg/5 μL) in ameliorating mechanical allodynia induced by a total of 4 paclitaxel injections (2 mg/kg, intraperitoneal). Again, 5bk resulted in a reversal of mechanical allodynia at two hours post-injection and lasting for at least two hours with a commensurate increase in area under the curve in comparison to saline-injected animals (FIG. 16G-I). Together, these results demonstrate that 5bk is antinociceptive in rodent models of neuropathic pain.

5bk Does Not Alter Motor Function or Anxiety Levels in Treated Animals

Since 5bk appears to be a promising anti-nociceptive agent in terms of neuropathic pain models, we next asked if the compound had any effects on motor function or anxiety in naive animals. To test for motor deficits, we subjected rats to a rotarod performance test. Compared to vehicle-treated rats, there was no significant change in motor function in animals treated with intrathecal 5bk. Vehicle-treated animals remained on the rotarod for an average of 172±7.3 seconds (cutoff time 180 seconds per test) over a time course of 300 minutes; 5bk-treated animals remained on the rotarod for an average of 170±9.6 seconds over a time-course of 300 minutes (FIG. 17A). From these results, we conclude that 5bk does not induce motor deficits.

To test if anxiety levels are affected by 5bk, we subjected naive rats to the elevated plus maze (EPM) test. The measured anxiety index integrates both measurement of times and entries of the animals into the open and closed arms of the EPM. Index values closer to 1 indicate higher anxiety levels. Results indicate that there was no significant change in anxiety index between animals treated with 5bk (2 μg/5 μL, i.t.) and those treated with the vehicle (FIG. 17B), and thus we conclude that 5bk is an antinociceptive agent that does not cause dysfunction in motor or anxiety-related measures.

Discussion

The present work used Ugi-azide MCR products to identify a selective antagonist of the T-type Ca2+channel CaV3.2. Of the 46 compounds tested, 5bk—a benzimidazolonepiperidine analog, interacted with the T-type Ca2+ channels in a stereospecific manner, specifically blocked T-type calcium channels in a concentration and time-dependent manner and preferentially inhibited the CaV3.2 isoform. 5bk inhibited spinal neurotransmission which resulted in a decrease in CGRP release from the spinal cord. Finally, 5bk had an anti-nociceptive effect in rodent models of neuropathic pain (FIG. 16 ) without inducing adverse side effects (FIG. 17 ). Taken together our findings indicate that the preferential inhibition of CaV3.2 channels results in a selective and safe antinociceptive effect.

During the biochemical characterization of 5bk, we came across a paper by Zhao et al. reporting the cryo-EM structure of the human apo CaV3.1 channel bound to the selective blocker Z944 [94]. We generated homology models of both CaV3.2 and CaV3.3 using the Phyre2 server. Structurally, the models are identical to CaV3.1 and we used the homology model structure of CaV3.2 to dock 5bk (FIG. 18 ). Closer inspection of 5bk and Z944 ({N}-[[1-[2-(˜{tert}-butylamino)-2-oxidanylidene-ethyl]piperidin-4-yl]methyl]-3-chloranyl-5-fluoranylbenzamide) T-type Ca2+ channel blockers revealed similar pharmacophore features (FIG. 18 , FIG. 19 ) presumably responsible for productive binding of both antagonists. Due to the extremely high sequence similarity in CaV3.1-3.3 in and around the binding cavity, we cannot conclude as to the exact residues that may confer selectivity of this compound. Notably, decoration of the common piperidine core would suggest a similar molecular shape within the channel cavity with functional groups pointing to the same areas (FIG. 19 ). Indeed, the 3-D overlay confirms the topological match of aligned scaffolds with carbonyl groups at the southern part of each molecule presented as a shared pharmacophore feature (FIG. 18B, FIG. 19 ). Similarly, the top carboxamide in Z944 overlaps with nitrogens in the tetrazole ring of 5bk, mimicking the amide bond of the former molecule. Phenyl and t-butyl groups from the corresponding molecules point in the same direction. However, the 3-thiophenyl group is not present in Z944, suggesting a hydrophobic pocket in that area that was explored during our lead compound optimization.

The presence of two chiral centers on 5bk gives rise to four possible enantiomers as two pairs of diastereomers. To simplify the structure elucidation of the bioactive stereoisomer, we utilized enantiomerically pure (1S)-methylbenzyl isocyanide as a reagent and separated resulting diastereomers by silica gel flash column chromatography. From the X-ray crystal structure, we found out that the relative configuration of the bioactive diastereomer is (1R, 2S) where the first descriptor refers to the chiral carbon bearing the 3-thiophenyl substituent. SAR obtained from analogs within the library of Ugi-azide MCR products suggests the possibility of replacing 4-aminopiperidine with a druglike N-acyl- or N-arylpiperazine scaffold. Moreover, SAR expansion in the thiophenyl area is expected to improve both potency and selectivity.

T-type Ca2+ channels were generally considered to regulate neuronal excitability at peripheral terminals of nociceptors, while high-voltage-activated (HVA) N- and P/Q-type Ca2+ channels regulate neurotransmitter release such as glutamate and substance P in the spinal cord [61]. The majority of studies examining T-type Ca2+ channels in the spinal cord have used less specific blockers such as ethosuximide [49], mibefradil [47] TTA-A2 and TTA-P2 [35] to determine the function of the channels. However, there is evidence indicating that CaV3.2 channels regulate low threshold exocytosis in cell cultures [85] and spontaneous release of glutamate in the spinal cord dorsal horn [35]. Unlike HVA Ca2+ channels, where several members of the vesicle release machinery interact with a synprint (synaptic protein interaction site) [62; 66], T-type Ca2+ channels lack the consensus synprint site, therefore, the neurotransmitter release machine interacts with the C-terminal domain of the CaV3.2 channels for neurotransmitter release [84]. In the present study we show that selective blockade of the CaV3.2 channels plays an important role in the excitatory synaptic transmission since 5bk inhibited the frequency but not the amplitude of sEPSCs (FIG. 14 ). A decrease in frequency suggests that 5bk inhibits glutamatergic excitatory inputs by a presynaptic mechanism. It is well accepted that alterations in the frequency of EPSCs with any agent targeting an ion channel indicates that this particular channel plays a presynaptic role, while changes in amplitude suggest a postsynaptic role of the channel. This is consistent with a previous report in which Jacus and colleagues demonstrated that CaV3.2 channels are the subtype of T-type Ca2+ channels responsible for presynaptic modulation of spontaneous synaptic transmission in lamina I and II [35]. Moreover, CaV3.2 channels appear not to participate in inhibitory synaptic transmission [35].

DRG neurons have been shown to differentially express T-type Ca2+ channels [64] with medium size neurons expressing the highest levels of CaV3.2 followed by the small size neurons [67]. T-type Ca2+ currents are present in ˜66 and ˜42% of medium and small neurons, belonging to lightly myelinated Aδ and unmyelinated C fibers, respectively [4]. Small C-type fiber nociceptors can be subdivided according to the expression of histological markers [68; 73]. One group are the peptidergic fibers that express proinflammatory peptides such as CGRP and substance P and project to the most superficial layers of the spinal cord dorsal horn, lamina I and the outer lamina II. A second group, the nonpeptidergic fibers, can be identified by the presence of binding sites for the isolectin B4 (IB4) and do not express substance P nor CGRP. These C fibers project to inner lamina II of the spinal cord dorsal horn [68]. Among these fibers, CaV3.2 expresses preferentially in the CGRP neurons and to a lesser extent in IB4 positive fibers [35]. Importantly, our findings show that that 5bk inhibited depolarization evoked CGRP release in spinal cord (FIG. 15 ), a known excitatory neurotransmitter that facilitates nociceptive transmission and contributes to central sensitization [68]. These results suggest a mechanism for the anti-nociceptive effect of 5bk (FIG. 16 ).

CaV3.2 channel expression and activity is increased in DRG neurons and in the spinal cord dorsal horn in neuropathic pain, such as in the L5 spinal nerve cut [74], L5/L6 SNL [29], chronic constriction injury (CCI)[36], diabetic neuropathy [37; 50], paclitaxel-induced peripheral neuropathy [44], spared nerve injury (SNI)[38], chronic compression of DRGs [86], and partial sciatic nerve ligation (PSNL)[20] rodent models. Although changes in the open probability of CaV3.2 cannot be ruled out, the most straightforward explanation for a change in current density, as we showed in our results (FIG. 5 ), is that 5bk decreases the cell surface or the protein expression of CaV3.2 channels. It is known that phosphorylation [5], glycosylation [83] and ubiquitylation [26] are two important post-translational regulation mechanisms that positively regulate surface expression of these channels.

It is also noteworthy that in neuropathic pain, there is a redistribution of the α2δ-1 HVA Ca2+ channels auxiliary subunit [2] and CaV3.2 channels [29] to the DRG of injured nerves. DRGs have been shown to be an ectopic activity generation sites that play an important role in the development and maintenance of neuropathic pain [45]. Similar to TRPV1 [25] and NaV1.8 channels [28], CaV3.2 channels are redistributed to uninjured nerves in neuropathic pain models. This contributes to spontaneous activity and suggests an important role in pain hypersensitivity [12; 46]. In our present study, we have demonstrated that selective blockade of CaV3.2 channels with 5bk reversed neuropathic pain (FIG. 16 ), which is consistent with previous reports of CaV3.2 silencing in DRGs of rats with CCI [4] and paclitaxel-induced peripheral neuropathy [38]. Interestingly, similar to mice lacking CaV3.2 [15], intrathecal administration of 5bk had no alterations in motor function or anxiety (FIG. 17 ). However, a limitation here is that since 5bk was administered intrathecally, it is possible that not enough of the compound may have reached the brain to engage CaV3.2 channels therein.

Finally, recent evidence from experiments involving recombinant T-channels indicate that the βγ subunit of G protein coupled receptors selectively inhibits the function of CaV3.2 channels by interacting with the intracellular loop connecting domains II and III and by decreasing single channel open probability [16]. Our findings suggested that 5bk did not target G-protein coupled opioid receptor signaling (FIG. 13 ). Thus, inhibition of Ca2+ influx by 5bk likely does not involve opioid receptors. Moreover, contrary to our previously identified CaV3.2 inhibitor betulinic acid [3], 5bk did not affect any of the high voltage-activated calcium channels including N-type (CaV2.2) (FIG. 6 ), hERG channel activity (FIG. 20 ), or sodium channel activity FIG. 8 ), which helps to confirm drug selectivity. In conclusion, the findings recited herein describe the identification of a new class of inhibitors of CaV3.2 T-type Ca2+ channels, which are promising candidates for efficacious, non-opioid pain therapeutics.

Example II

This example describes the compound synthesis and characterization.

Chemistry

Chemicals were ordered from commercial sources and were used without further purification. Synthesis procedures for reactions described in Scheme 1 were shown below. All final compounds were purified by flash column chromatography. 1H and 13C NMR spectra were recorded on a Bruker-400 NMR spectrometer. Chemical shifts are reported in parts per million referenced with respect to residual solvent (CD3OD) 3.31 ppm, (DMSO-d6) 2.50 ppm, and (CDCl3) 7.24 ppm or from internal standard tetramethylsilane (TMS) 0.00 ppm. The following abbreviations were used in reporting spectra: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; dd, doublet of doublets; ddd, doublet of doublet of doublets. All reactions were carried out under N2 atmosphere unless otherwise stated. HPLC-grade solvents were used for all reactions. Flash column chromatography was performed using silica gel (230-400 mesh, Merck).

Low-resolution mass spectra were obtained using an ESI technique on a 3200 Q Trap LC/MS/MS system (Applied Biosystems). The purity was assessed by using a Shimadzu LC-MS with a Waters XTerra MS C-18 column (part no. 186000538), 50 mm×2.1 mm, at a flow rate of 0.3 mL/min; λ=250 and 220 nm; mobile phase A, 0.1% formic acid in H2O, and mobile phase B′, 0.1% formic in 60% 2-propanol, 30% CH3CN, and 9.9% H2O. All compounds submitted for mechanistic studies were confirmed to be >95.0% purity by LC-MS traces.

Synthesis Procedures. General Procedure for the Synthesis of Tetrazole.

Aldehyde (1 mmol) and amine (1 mmol) were added to methanol (5 ml). The solution was stirred at room temperature for 10 mins. Then TMS-N3 (1 mmol) and isocyanide (1 mmol) were added sequentially. The mixture was stirred at room temperature overnight. Solvent was removed by rotatory evaporation and the crude product was purified by flash column chromatography (20-100% ethyl acetate/hexane) to give the final product.

1-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl](5-methylthiophen-2-yl)methyl}-4-(furan-2-carbonyl)piperazine. (5aa). Yield: 90.6%. 1H NMR (400 MHz, CDCl3) δ 7.51-7.33 (m, 2H), 7.29-7.20 (m, 1H), 7.20-7.09 (m, 1H), 6.94 (dd, J=3.4, 0.9 Hz, 1H), 6.66 (d, J=3.5 Hz, 1H), 6.56 (dt, J=3.6, 1.2 Hz, 1H), 6.44 (dd, J=3.4, 1.8 Hz, 1H), 4.70 (s, 1H), 3.88-3.60 (m, 4H), 2.85-2.62 (m, 2H), 2.58-2.45 (m, 2H), 2.43 (s, 3H), 2.05 (s, 3H), 1.53 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 158.92, 154.74, 147.71, 143.72, 142.24, 136.41, 135.63, 132.82, 131.48, 131.18, 129.07, 128.96, 128.92, 124.78, 116.54, 111.29, 58.95, 50.27, 17.70, 16.95, 15.36.

C24H26N6O2S, EI-MS: m/z (M+H+): 463.6 (calculated), 463.6 (found).

1-(furan-2-carbonyl)-4-[(5-methylthiophen-2-yl)({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl]piperazine. (5ab). Yield: 71.9%. 1H NMR (400 MHz, CDCl3) δ 7.46-7.38 (m, 1H), 7.38-7.27 (m, 3H), 7.24-7.12 (m, 2H), 6.92 (dd, J=3.5, 0.8 Hz, 0.5H), 6.88 (dd, J=3.5, 0.9 Hz, 0.5H), 6.64 (d, J=3.5 Hz, 0.5H), 6.60 (dd, J=3.2, 0.8 Hz, 1H), 6.54-6.49 (m, 0.5H), 6.45-6.36 (m, 1H), 6.08 (q, J=7.1 Hz, 0.5H), 5.54 (q, J=7.0 Hz, 0.5H), 5.11 (s, 0.5H), 5.06 (s, 0.5H), 3.77-3.44 (m, 4H), 2.67-2.53 (m, 1H), 2.53-2.40 (m, 4H), 2.40-2.23 (m, 2H), 2.02-1.89 (m, 3H). 13C NMR (101 MHz, CDCl3) δ 158.94, 158.88, 153.52, 153.32, 147.80, 147.77, 143.76, 143.67, 142.05, 141.78, 139.73, 139.23, 132.92, 132.90, 129.26, 129.16, 129.04, 128.77, 128.67, 128.61, 126.33, 126.10, 124.90, 124.79, 116.64, 116.43, 111.35, 111.27, 60.35, 59.35, 59.11, 58.84, 50.53, 49.66, 22.79, 15.42, 15.37. C24H26N6O2S, EI-MS: m/z (M+H+): 463.6 (calculated), 463.6 (found).

1-[(1-benzyl-1H-1,2,3,4-tetrazol-5-yl)(5-methylthiophen-2-yl)methyl]-4-(furan-2-carbonyl)piperazine. (5ac). Yield: 74.9%. 1H NMR (400 MHz, CDCl3) δ 7.42 (dd, J=1.8, 0.9 Hz, 1H), 7.39-7.28 (m, 3H), 7.20-7.09 (m, 2H), 6.93 (dd, J=3.5, 0.8 Hz, 1H), 6.64 (d, J=3.5 Hz, 1H), 6.58 (dt, J=3.5, 1.1 Hz, 1H), 6.43 (dd, J=3.5, 1.7 Hz, 1H), 5.74 (d, J=15.4 Hz, 1H), 5.48 (d, J=15.4 Hz, 1H), 5.07 (s, 1H), 3.76-3.58 (m, 4H), 2.67-2.51 (m, 2H), 2.43 (s, 3H), 2.44-2.32 (m, 2H). 13C NMR (101 MHz, CDCl3) δ 158.97, 153.78, 147.82, 143.77, 142.04, 133.42, 132.58, 129.30, 129.07, 128.91, 127.52, 124.93, 116.66, 111.38, 59.72, 51.55, 50.09, 15.43. C23H24N6O2S, EI-MS: m/z (M+H+): 449.5 (calculated), 449.5 (found).

1-[(1-cyclohexyl-1H-1,2,3,4-tetrazol-5-yl)(5-methylthiophen-2-yl)methyl]-4-(furan-2carbonyl)piperazine. (5ad). Yield: 85.1%. 1H NMR (400 MHz, CDCl3) δ 7.43 (dd, J=1.8, 0.9 Hz, 1H), 6.96 (dd, J=3.5, 0.9 Hz, 1H), 6.77 (d, J=3.5 Hz, 1H), 6.60 (dq, J=3.4, 1.1 Hz, 1H), 6.44 (dd, J=3.5, 1.8 Hz, 1H), 5.26 (s, 1H), 4.57-4.39 (m, 1H), 3.96-3.59 (m, 4H), 2.78-2.66 (m, 2H), 2.62-2.47 (m, 2H), 2.45 (s, 3H), 2.13-1.85 (m, 6H), 1.85-1.64 (m, 2H), 1.48-1.30 (m, 2H). 13C NMR (101 MHz, CDCl3) δ 159.08, 152.64, 147.84, 143.80, 141.89, 133.91, 128.65, 124.97, 116.75, 111.41, 60.23, 58.55, 50.63, 33.15, 33.10, 25.56, 25.50, 24.91, 15.46. C22H28N6O2S, EI-MS: m/z (M+H+): 441.6 (calculated), 441.6 (found).

1-(furan-2-carbonyl)-4-({1-[(4-methylbenzenesulfonyl)methyl]-1H-1,2,3,4-tetrazol-5-yl}(5-methylthiophen-2-yl)methyl)piperazine. (5ae). Yield: 80.9%. 1H NMR (400 MHz, CDCl3) δ 7.58-7.46 (m, 2H), 7.43 (dd, J=1.8, 0.9 Hz, 1H), 7.36-7.28 (m, 2H), 6.95 (dd, J=3.5, 0.9 Hz, 1H), 6.84 (d, J=3.5 Hz, 1H), 6.72-6.60 (m, 1H), 6.43 (dd, J=3.5, 1.8 Hz, 1H), 6.15 (d, J=14.4 Hz, 1H), 5.73 (s, 1H), 5.55 (d, J=14.4 Hz, 1H), 4.00-3.66 (m, 4H), 2.75-2.55 (m, 4H), 2.47 (s, 3H), 2.44 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 158.95, 154.97, 147.74, 147.05, 143.80, 142.27, 132.28, 130.56, 130.20, 129.81, 128.95, 124.99, 116.73, 111.37, 65.89, 59.41, 49.56, 21.90, 15.40. C24H26N6O4S2, EI-MS: m/z (M+H+): 527.6 (calculated), 527.4 (found).

1-(furan-2-carbonyl)-4-[(5-methylthiophen-2-yl)(1-pentyl-1H-1,2,3,4-tetrazol-5-yl)methyl]piperazine. (5af). Yield: 62.3%. 1H NMR (400 MHz, CDCl3) δ 7.43 (dd, J=1.8, 0.9 Hz, 1H), 6.96 (dd, J=3.5, 0.9 Hz, 1H), 6.78 (d, J=3.5 Hz, 1H), 6.61 (dq, J=3.4, 1.1 Hz, 1H), 6.44 (dd, J=3.5, 1.8 Hz, 1H), 5.28 (s, 1H), 4.44-4.26 (m, 2H), 3.95-3.68 (m, 4H), 2.88-2.72 (m, 2H), 2.65-2.49 (m, 2H), 2.44 (s, 3H), 1.93-1.76 (m, 2H), 1.40-1.22 (m, 4H), 0.87 (t, J=6.9 Hz, 3H). 13C NMR (101 MHz, CDCl3) δ 159.00, 153.19, 147.76, 143.83, 142.19, 128.97, 125.04, 116.79, 111.42, 59.74, 50.36, 48.01, 29.32, 28.67, 22.18, 15.44, 13.90. C21H28N6O2S, EI-MS: m/z (M+H+): 429.6 (calculated), 429.5 (found).

1-(furan-2-carbonyl)-4-[(5-methylthiophen-2-yl)[1-(naphthalen-2-yl)-1H-1,2,3,4-tetrazol-5-yl]methyl]piperazine. (5ag). Yield: 74.5%. 1H NMR (400 MHz, CDCl3) δ 8.03 (dt, J=8.6, 0.7 Hz, 1H), 8.01-7.91 (m, 2H), 7.91-7.82 (m, 1H), 7.71-7.59 (m, 2H), 7.50 (dd, J=8.7, 2.2 Hz, 1H), 7.43 (dd, J=1.8, 0.9 Hz, 1H), 6.95 (dd, J=3.4, 0.9 Hz, 1H), 6.79 (d, J=3.5 Hz, 1H), 6.63 (dq, J=3.3, 1.0 Hz, 1H), 6.44 (dd, J=3.5, 1.8 Hz, 1H), 5.26 (s, 1H), 3.92-3.64 (m, 4H), 2.94-2.69 (m, 2H), 2.65-2.50 (m, 2H), 2.47 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 159.01, 147.77, 143.79, 133.74, 132.86, 130.82, 130.37, 128.50, 128.33, 128.18, 128.02, 125.02, 124.68, 122.37, 116.69, 111.38, 58.67, 49.67, 15.48. C26H24N6O2S, EI-MS: m/z (M+H+): 485.6 (calculated), 485.6 (found).

1-[(1-tert-butyl-1H-1,2,3,4-tetrazol-5-yl)(5-methylthiophen-2-yl)methyl]-4-(furan-2-carbonyl)piperazine. (5ah). Yield: 79.3%. 1H NMR (400 MHz, CDCl3) δ 7.42 (dd, J=1.8, 0.9 Hz, 1H), 6.94 (dd, J=3.4, 0.9 Hz, 1H), 6.65 (d, J=3.5 Hz, 1H), 6.57 (dq, J=3.4, 1.1 Hz, 1H), 6.43 (dd, J=3.5, 1.8 Hz, 1H), 5.57 (s, 1H), 3.91-3.63 (m, 4H), 3.01-2.81 (m, 2H), 2.66-2.52 (m, 2H), 2.44 (s, 3H), 1.73 (s, 9H). 13C NMR (101 MHz, CDCl3) δ 159.02, 153.29, 147.85, 143.74, 142.21, 129.12, 124.75, 116.57, 111.34, 61.78, 60.10, 49.89, 30.26, 15.44. C20H26N6O2S, EI-MS: m/z (M+H+): 415.5 (calculated), 415.3 (found).

1-(furan-2-carbonyl)-4-{[1-(4-methoxyphenyl)-1H-1,2,3,4-tetrazol-5-yl](5-methylthiophen-2-yl)methyl}piperazine. (5ai). Yield: 79.5%. 1H NMR (400 MHz, CDCl3) δ 7.42 (dd, J=1.8, 0.9 Hz, 1H), 7.34-7.27 (m, 2H), 7.08-6.99 (m, 2H), 6.94 (dd, J=3.5, 0.9 Hz, 1H), 6.76-6.68 (m, 1H), 6.63-6.55 (m, 1H), 6.43 (dd, J=3.5, 1.8 Hz, 1H), 5.14 (s, 1H), 3.88 (s, 3H), 3.84-3.66 (m, 4H), 2.92-2.71 (m, 2H), 2.56-2.47 (m, 2H), 2.45 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 161.36, 159.01, 153.45, 147.81, 143.78, 128.94, 126.95, 126.07, 124.96, 116.64, 115.10, 111.37, 58.60, 55.84, 49.73, 15.46. C23H24N6O3S, EI-MS: m/z (M+H+): 465.5 (calculated), 465.4 (found).

1-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl](5-methylfuran-2-yl)methyl}-4-(furan-2-carbonyl)piperazine. (5aj). Yield: 85.3%. 1H NMR (400 MHz, CDCl3) δ 7.43 (dd, J=1.8, 0.9 Hz, 1H), 7.37 (t, J=7.6 Hz, 1H), 7.25-7.21 (m, 1H), 7.18-7.13 (m, 1H), 6.93 (dd, J=3.5, 0.9 Hz, 1H), 6.43 (dd, J=3.5, 1.8 Hz, 1H), 6.33 (dt, J=3.2, 0.5 Hz, 1H), 5.92-5.87 (m, 1H), 3.81-3.67 (m, 4H), 2.90-2.77 (m, 2H), 2.52-2.38 (m, 2H), 2.22 (s, 3H), 2.04 (s, 3H), 1.64 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 159.02, 153.55, 153.32, 147.80, 145.02, 143.79, 136.13, 136.00, 131.69, 131.17, 128.96, 116.63, 112.98, 111.36, 106.74, 56.79, 50.28, 17.77, 17.10, 13.74. C24H26N6O3, EI-MS: m/z (M+H+): 447.5 (calculated), 447.5 (found).

1-(furan-2-carbonyl)-4-{[5-(methylsulfanyl)thiophen-2-yl]({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl}piperazine. (5ak). Yield: 79.6%. 1H NMR (400 MHz, CDCl3) δ 7.47-7.40 (m, 1H), 7.40-7.25 (m, 3H), 7.25-7.11 (m, 2H), 6.95 (dd, J=3.5, 0.8 Hz, 0.5H), 6.93-6.84 (m, 1H), 6.80 (d, J=3.7 Hz, 0.5H), 6.73 (d, J=3.6 Hz, 0.5H), 6.62 (d, J=3.7 Hz, 0.5H), 6.49-6.36 (m, 1H), 6.04 (q, J=7.0 Hz, 0.5H), 5.64 (q, J=7.0 Hz, 0.5H), 5.15 (s, 0.5H), 5.13 (s, 0.5H), 3.85-3.65 (m, 2H), 3.65-3.42 (m, 2H), 2.68-2.56 (m, 1H), 2.49 (s, 1.5H), 2.47 (s, 1.5H), 2.53-2.32 (m, 3H), 2.12-1.95 (m, 3H). 13C NMR (101 MHz, CDCl3) δ 158.93, 158.85, 152.98, 152.81, 147.69, 147.67, 143.80, 143.71, 139.94, 139.64, 139.60, 139.08, 137.03, 137.01, 129.69, 129.46, 129.26, 129.23, 129.22, 128.91, 128.78, 126.22, 126.07, 116.73, 116.53, 111.37, 111.29, 60.08, 59.28, 59.18, 58.94, 50.34, 49.56, 22.84, 22.69, 21.65, 21.50. C24H26N6O2S2, EI-MS: m/z (M+H+): 495.6 (calculated), 495.8 (found).

1-(furan-2-carbonyl)-4-({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl}(thiophen-2-yl)methyl)piperazine. (5al). Yield: 78.4%. 1H NMR (400 MHz, CDCl3) δ 7.48-7.39 (m, 1H), 7.39-7.24 (m, 4H), 7.24-7.12 (m, 2H), 7.02-6.90 (m, 1.5H), 6.90-6.84 (m, 1H), 6.84-6.77 (m, 0.5H), 6.49-6.35 (m, 1H), 6.10 (q, J=7.0 Hz, 0.5H), 5.68 (q, J=7.0 Hz, 0.5H), 5.28 (s, 1H), 3.82-3.63 (m, 2H), 3.63-3.35 (m, 2H), 2.71-2.52 (m, 1H), 2.52-2.29 (m, 3H), 2.01-1.89 (m, 3H). 13C NMR (101 MHz, CDCl3) δ 158.75, 158.66, 153.25, 153.04, 147.51, 147.50, 143.66, 143.57, 139.63, 138.94, 135.32, 135.16, 129.04, 128.99, 128.77, 128.59, 128.53, 127.02, 126.79, 126.61, 126.54, 126.14, 125.96, 116.40, 116.21, 111.18, 111.10, 59.56, 58.89, 58.69, 58.66, 50.19, 49.33, 22.67, 22.50. C23H24N6O2S, EI-MS: m/z (M+H+): 449.5 (calculated), 449.6 (found).

1-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl](thiophen-2-yl)methyl}-4-(furan-2 carbonyl)piperazine. (5am). Yield: 86.4%. 1H NMR (400 MHz, CDCl3) δ 7.42 (dd, J=1.8, 0.9 Hz, 1H), 7.39 (t, J=7.6 Hz, 1H), 7.34-7.28 (m, 1H), 7.28-7.21 (m, 1H), 7.17-7.09 (m, 1H), 6.98-6.88 (m, 3H), 6.43 (dd, J=3.5, 1.8 Hz, 1H), 4.81 (s, 1H), 3.94-3.64 (m, 4H), 2.90-2.66 (m, 2H), 2.57-2.42 (m, 2H), 2.05 (s, 3H), 1.48 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 158.98, 154.69, 147.82, 143.80, 136.48, 135.75, 135.37, 131.50, 131.32, 129.28, 129.08, 129.06, 127.59, 126.93, 116.70, 111.40, 58.74, 50.38, 17.83, 16.96. C23H24N6O2S, EI-MS: m/z (M+H+): 449.5 (calculated), 449.5 (found).

1-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl] (thiophen-3-yl)methyl}-4-(furan-2-carbonyl)piperazine. (5an). Yield: 81.6%. 1H NMR (400 MHz, CDCl3) δ 7.42 (dd, J=1.8, 0.9 Hz, 1H), 7.38 (t, J=7.6 Hz, 1H), 7.30-7.20 (m, 2H), 7.15-7.02 (m, 3H), 6.95 (dd, J=3.5, 0.9 Hz, 1H), 6.44 (dd, J=3.5, 1.8 Hz, 1H), 4.59 (s, 1H), 3.91-3.66 (m, 4H), 2.81-2.56 (m, 2H), 2.56-2.36 (m, 2H), 2.03 (s, 3H), 1.36 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 158.97, 147.84, 143.80, 136.62, 135.53, 131.55, 131.25, 129.06, 129.00, 128.13, 126.89, 116.71, 111.41, 59.43, 50.84, 17.80, 16.75. C23H24N6O2S, EI-MS: m/z (M+H+): 449.5 (calculated), 449.5 (found).

1-(furan-2-carbonyl)-4-[phenyl({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl]piperazine. (5ao). Yield: 68.9%. 1H NMR (400 MHz, CDCl3) δ 7.47-7.38 (m, 1H), 7.38-7.27 (m, 6H), 7.27-7.18 (m, 2H), 7.17-7.05 (m, 2H), 6.96-6.84 (m, 1H), 6.47-6.35 (m, 1H), 5.93 (q, J=7.0 Hz, 0.5H), 5.47 (q, J=7.1 Hz, 0.5H), 4.92 (s, 0.5H), 4.79 (s, 0.5H), 3.82-3.50 (m, 4H), 2.69-2.55 (m, 0.5H), 2.49-2.26 (m, 3.5H), 1.96-1.81 (m, 3H). 13C NMR (101 MHz, CDCl3) δ 158.82, 158.74, 154.00, 153.62, 147.64, 143.67, 143.59, 139.47, 138.82, 133.71, 133.60, 129.16, 128.97, 128.92, 128.87, 128.66, 128.62, 128.60, 128.50, 126.30, 125.95, 116.43, 116.27, 111.22, 111.16, 64.55, 64.44, 58.59, 58.52, 53.49, 50.87, 50.37, 22.45, 22.43. C25H26N6O2, EI-MS: m/z (M+H+): 443.5 (calculated), 443.6 (found).

1-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl](2-methylphenyl)methyl}-4-(furan-2-carbonyl)piperazine. (5ap). Yield: 76.3%. 1H NMR (400 MHz, CDCl3) δ 7.42 (dd, J=1.8, 0.9 Hz, 1H), 7.40-7.29 (m, 2H), 7.26-7.19 (m, 1H), 7.17-7.04 (m, 2H), 7.04-6.98 (m, 2H), 6.96 (dd, J=3.4, 0.9 Hz, 1H), 6.44 (dd, J=3.5, 1.8 Hz, 1H), 4.64 (s, 1H), 3.86 (s, 4H), 2.77-2.64 (m, 2H), 2.62-2.50 (m, 2H), 2.00 (s, 3H), 1.68 (s, 3H), 0.97 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 158.96, 156.13, 147.86, 143.78, 137.37, 137.32, 134.93, 131.48, 131.26, 130.76, 130.14, 129.11, 128.83, 126.86, 116.65, 111.38, 60.73, 51.29, 18.72, 17.69, 16.19. C26H28N6O2, EI-MS: m/z (M+H+): 457.6 (calculated), 457.6 (found).

1-(furan-2-carbonyl)-4-({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl}(thian-4-yl)methyl)piperazine. (5aq). Yield: 62.8%. 1H NMR (400 MHz, CDCl3) δ 7.48-7.24 (m, 5H), 7.23-7.12 (m, 1H), 6.95 (dd, J=3.5, 0.9 Hz, 0.5H), 6.86 (dd, J=3.4, 0.9 Hz, 0.5H), 6.50-6.35 (m, 1H), 5.63-5.45 (m, 1H), 4.00-3.35 (m, 5H), 2.76-2.33 (m, 7H), 2.33-1.98 (m, 6H), 1.50-1.22 (m, 2H), 0.90-0.76 (m, 0.5H), 0.40-0.17 (m, 0.5H). 13C NMR (101 MHz, CDCl3) δ 159.01, 158.94, 152.38, 151.30, 147.70, 143.81, 143.67, 139.65, 139.61, 129.39, 129.36, 129.09, 128.99, 126.37, 126.18, 116.79, 116.40, 111.41, 111.27, 63.43, 63.06, 59.03, 58.75, 38.85, 37.99, 31.90, 31.41, 31.07, 28.48, 28.34, 28.27, 28.06, 23.68, 22.95. C24H30N6O2S, EI-MS: m/z (M+H+): 467.6 (calculated), 467.6 (found).

1-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl](phenyl)methyl}-4-(furan-2-carbonyl)piperazine. (5ar). Yield: 90.3%. 1H NMR (400 MHz, CDCl3) δ 7.42 (dd, J=1.8, 0.9 Hz, 1H), 7.37 (t, J=7.6 Hz, 1H), 7.31-7.18 (m, 4H), 7.17-7.10 (m, 2H), 7.09-7.02 (m, 1H), 6.95 (dd, J=3.5, 0.9 Hz, 1H), 6.43 (dd, J=3.5, 1.8 Hz, 1H), 4.38-4.24 (m, 1H), 4.01-3.67 (m, 4H), 2.70-2.45 (m, 4H), 2.02 (s, 3H), 1.09 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 158.95, 147.87, 143.78, 136.94, 135.03, 131.48, 131.25, 129.54, 129.24, 129.07, 128.94, 128.90, 116.68, 111.40, 65.35, 51.52, 17.76, 16.60. C25H26N6O2, EI-MS: m/z (M+H+): 443.5 (calculated), 443.6 (found).

1-{1-[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl]-2-phenylethyl}-4-(furan-2-carbonyl)piperazine. (5as). Yield: 83.9%. 1H NMR (400 MHz, CDCl3) δ 7.46 (dd, J=1.8, 0.9 Hz, 1H), 7.31 (t, J=7.6 Hz, 1H), 7.22-7.06 (m, 6H), 7.06-6.94 (m, 2H), 6.47 (dd, J=3.5, 1.8 Hz, 1H), 3.90-3.56 (m, 5H), 3.54-3.39 (m, 1H), 3.13 (dd, J=12.6, 3.2 Hz, 1H), 3.07-2.91 (m, 2H), 2.62-2.45 (m, 2H), 2.07 (s, 3H), 0.97 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 159.18, 154.40, 147.85, 143.82, 137.57, 136.77, 135.74, 131.59, 130.93, 129.71, 128.76, 128.62, 128.60, 126.83, 116.73, 111.43, 61.90, 48.85, 31.36, 17.91, 15.76. C26H28N6O2, EI-MS: m/z (M+H+): 457.6 (calculated), 457.6 (found).

1-(furan-2-carbonyl)-4-(2-phenyl-1-{1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl}ethyl)piperazine. (5at). Yield: 70.9%. 1H NMR (400 MHz, CDCl3) δ 7.48-7.41 (m, 1H), 7.35-7.14 (m, 5H), 7.12-6.95 (m, 4H), 6.93-6.83 (m, 2H), 6.51-6.37 (m, 1H), 5.69 (q, J=7.0 Hz, 0.5H), 4.89 (q, J=7.0 Hz, 0.5H), 4.09-3.95 (m, 1H), 3.84-3.64 (m, 2H), 3.56-3.42 (m, 2H), 3.41-3.30 (m, 1H), 3.26-3.11 (m, 1H), 2.77-2.68 (m, 1H), 2.66-2.57 (m, 1H), 2.54-2.29 (m, 2H), 1.94 (d, J=7.0 Hz, 1.5H), 1.65 (d, J=7.0 Hz, 1.5H). 13C NMR (101 MHz, CDCl3) δ 159.11, 158.96, 153.62, 152.95, 147.81, 143.85, 143.73, 139.92, 139.20, 137.36, 137.28, 129.32, 129.22, 129.14, 129.07, 128.86, 128.62, 128.52, 128.49, 127.06, 126.54, 126.12, 125.86, 116.78, 116.53, 111.44, 111.34, 61.69, 61.05, 58.44, 58.31, 35.78, 33.07, 22.56, 22.17. C26H28N6O2. EI-MS: m/z (M+H+): 457.6 (calculated), 457.6 (found).

1-[1-(1-benzyl-1H-1,2,3,4-tetrazol-5-yl)-2-phenylethyl]-4-(furan-2-carbonyl)piperazine. (5au). Yield: 87.3%. 1H NMR (400 MHz, CDCl3) δ 7.50-7.40 (m, 1H), 7.36-7.21 (m, 3H), 7.21-7.09 (m, 3H), 7.04-6.88 (m, 5H), 6.51-6.40 (m, 1H), 5.38 (d, J=15.5 Hz, 1H), 5.00 (d, J=15.5 Hz, 1H), 4.03 (dd, J=10.6, 3.9 Hz, 1H), 3.76-3.48 (m, 4H), 3.37 (dd, J=13.0, 10.6 Hz, 1H), 3.20 (dd, J=13.0, 3.9 Hz, 1H), 2.69-2.42 (m, 4H). 13C NMR (101 MHz, CDCl3) δ 159.06, 153.70, 147.85, 143.81, 137.30, 133.55, 129.26, 129.22, 128.86, 128.79, 127.31, 126.92, 116.71, 111.42, 61.40, 50.80, 49.20, 34.46. C25H26N6O2, EI-MS: m/z (M+H+): 443.5 (calculated), 443.6 (found).

1-(furan-2-carbonyl)-4-(1-{1-[(4-methylbenzenesulfonyl)methyl]-1H-1,2,3,4-tetrazol-5-yl}-2-phenylethyl)piperazine. (5av). Yield: 74.8%. 1H NMR (400 MHz, CDCl3) δ 7.46 (dd, J=1.8, 0.9 Hz, 1H), 7.34-7.13 (m, 9H), 6.98 (dd, J=3.5, 0.9 Hz, 1H), 6.46 (dd, J=3.5, 1.8 Hz, 1H), 5.75 (d, J=14.4 Hz, 1H), 5.36 (d, J=14.4 Hz, 1H), 4.80 (dd, J=9.6, 4.7 Hz, 1H), 3.93-3.60 (m, 4H), 3.52-3.38 (m, 1H), 3.38-3.23 (m, 1H), 2.90-2.64 (m, 4H), 2.39 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 159.02, 155.08, 147.72, 146.81, 143.83, 137.38, 131.73, 130.39, 129.61, 128.72, 128.67, 126.89, 116.72, 111.39, 65.48, 60.58, 49.05, 32.77, 21.82. C26H28N6O4S. EIMS: m/z (M+H+): 521.6 (calculated), 521.6 (found).

1-(furan-2-carbonyl)-4-(2-phenyl-1-{1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl}ethyl)piperazine. (5aw). Yield: 70.8%. 1H NMR (400 MHz, CDCl3) δ 7.53-7.37 (m, 1H), 7.35-7.14 (m, 5H), 7.14-6.96 (m, 4H), 6.96-6.78 (m, 2H), 6.54-6.38 (m, 1H), 5.68 (q, J=7.1 Hz, 0.5H), 4.88 (q, J=7.0 Hz, 0.5H), 4.11-3.93 (m, 1H), 3.88-3.60 (m, 2H), 3.60-3.41 (m, 2H), 3.41-3.28 (m, 1H), 3.28-3.07 (m, 1H), 2.84-2.67 (m, 1H), 2.67-2.56 (m, 1H), 2.57-2.28 (m, 2H), 1.94 (d, J=7.1 Hz, 1.5H), 1.64 (d, J=7.0 Hz, 1.5H). 13C NMR (101 MHz, CDCl3) δ 159.13, 158.98, 153.63, 152.96, 147.82, 143.86, 143.75, 139.93, 139.21, 137.37, 137.29, 129.33, 129.24, 129.16, 129.08, 128.88, 128.64, 128.54, 128.51, 127.08, 126.55, 126.13, 125.87, 116.81, 116.56, 114.36, 111.46, 111.36, 61.72, 61.07, 58.46, 58.34, 49.13, 35.82, 33.08, 22.58, 22.18. C26H28N6O2, EI-MS: m/z (M+H+): 457.6 (calculated), 457.6 (found).

1-[(5-methylthiophen-2-yl)({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl]-4-(pyridin-2-yl)piperazine. (5ax). Yield: 87.9%. 1H NMR (400 MHz, CDCl3) δ 8.21-8.06 (m, 1H), 7.49-7.37 (m, 1H), 7.37-7.13 (m, 5H), 6.68 (dd, J=3.6, 1.3 Hz, 1H), 6.65-6.46 (m, 3H), 6.18 (q, J=7.1 Hz, 0.5H), 5.66 (q, J=7.0 Hz, 0.5H), 5.13 (s, 0.5H), 5.10 (s, 0.5H), 3.52-3.26 (m, 4H), 2.67-2.58 (m, 1H), 2.56-2.48 (m, 1H), 2.49-2.30 (m, 5H), 2.05-1.91 (m, 3H). 13C NMR (101 MHz, CDCl3) δ 159.24, 159.22, 153.70, 153.47, 147.95, 147.90, 141.79, 141.51, 139.60, 139.37, 137.53, 137.47, 133.53, 133.05, 129.15, 129.12, 128.91, 128.66, 128.61, 128.43, 126.44, 126.27, 124.81, 124.69, 113.54, 113.32, 107.12, 107.00, 60.65, 59.73, 59.06, 58.73, 50.23, 49.65, 45.08, 44.99, 22.84, 22.77, 15.40, 15.37. C24H27N7S, EI-MS: m/z (M+H+): 446.6 (calculated), 446.8 (found).

1-[(5-methylthiophen-2-yl)({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl]-4-[3-(trifluoromethyl)pyridin-2-yl]piperazine. (5ay). Yield: 74.6%. 1H NMR (400 MHz, CDCl3) δ 8.49-8.32 (m, 1H), 7.90-7.74 (m, 1H), 7.43-7.22 (m, 5H), 7.04-6.88 (m, 1H), 6.77-6.67 (m, 1H), 6.64-6.53 (m, 1H), 6.22 (q, J=7.1 Hz, 0.5H), 5.74 (q, J=7.0 Hz, 0.5H), 5.14 (s, 0.5H), 5.12 (s, 0.5H), 3.33-3.11 (m, 4H), 2.73-2.54 (m, 2H), 2.54-2.39 (m, 5H), 2.11-1.94 (m, 3H). 13C NMR (101 MHz, CDCl3) δ 159.39, 159.22, 153.81, 153.53, 151.08, 150.98, 141.78, 141.50, 139.57, 139.45, 137.34, 137.29, 134.14, 133.20, 129.15, 128.87, 128.66, 128.64, 128.29, 126.51, 126.37, 124.82, 124.70, 117.08, 116.72, 116.60, 116.46, 60.68, 59.92, 59.09, 58.73, 50.48, 50.46, 50.31, 50.11, 22.89, 22.78, 15.43, 15.41. C25H26F3N7S, EI-MS: m/z (M+H+): 514.6 (calculated), 514.6 (found).

1-benzoyl-4-[(1-benzyl-1H-1,2,3,4-tetrazol-5-yl)(5-methylthiophen-2-yl)methyl]piperazine. (5az). Yield: 80.4%. 1H NMR (400 MHz, CDCl3) δ 7.47-7.28 (m, 8H), 7.20-7.03 (m, 2H), 6.69-6.49 (m, 2H), 5.73 (d, J=15.4 Hz, 1H), 5.45 (d, J=15.4 Hz, 1H), 5.07 (s, 1H), 3.87-3.03 (m, 4H), 2.68-2.48 (m, 2H), 2.45 (s, 3H), 2.43-2.17 (m, 2H). 13C NMR (101 MHz, CDCl3) δ 170.29, 153.71, 142.06, 135.55, 133.40, 132.80, 129.86, 129.30, 129.08, 128.83, 128.54, 127.52, 127.15, 124.94, 59.65, 51.52, 49.96, 15.45. C25H26N6OS, EI-MS: m/z (M+H+): 459.6 (calculated), 459.4 (found).

1-benzoyl-4-[(5-methylthiophen-2-yl)({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl]piperazine. (5ba). Yield: 81.7%. 1H NMR (400 MHz, CDCl3) δ 7.48-7.23 (m, 8H), 7.22-7.11 (m, 2H), 6.67-6.59 (m, 1H), 6.59-6.56 (m, 0.5H), 6.54-6.48 (m, 0.5H), 6.06 (q, J=7.0 Hz, 0.5H), 5.53 (q, J=7.0 Hz, 0.5H), 5.13 (s, 0.5H), 5.07 (s, 0.5H), 3.80-3.45 (m, 2H), 3.42-3.05 (m, 2H), 2.66-2.44 (m, 2H), 2.45 (s, 1.5H), 2.42 (s, 1.5H), 2.43-2.17 (m, 2H), 2.03-1.93 (m, 3H). 13C NMR (101 MHz, CDCl3) δ 170.25, 170.16, 153.46, 153.24, 142.06, 141.77, 139.70, 139.13, 135.56, 135.43, 133.21, 132.97, 129.84, 129.73, 129.26, 129.13, 128.98, 128.76, 128.66, 128.50, 128.44, 127.08, 127.06, 126.31, 126.07, 124.89, 124.77, 60.24, 59.25, 59.06, 58.82, 50.37, 22.73, 22.70, 15.42, 15.36. C26H28N6OS, EI-MS: m/z (M+H+): 473.6 (calculated), 473.6 (found).

1-benzoyl-4-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl](5-methylthiophen-2-yl)methyl}piperazine. (5bb). Yield: 78.3%. 1H NMR (400 MHz, CDCl3) δ 7.45-7.30 (m, 6H), 7.26-7.22 (m, 1H), 7.18-7.08 (m, 1H), 6.74-6.60 (m, 1H), 6.60-6.50 (m, 1H), 4.70 (s, 1H), 3.88-3.58 (m, 2H), 3.58-3.26 (m, 2H), 2.83-2.65 (m, 2H), 2.55-2.31 (m, 2H), 2.42 (s, 3H), 2.04 (s, 3H), 1.53 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 170.32, 154.75, 142.33, 136.56, 135.78, 135.60, 133.02, 131.61, 131.25, 129.87, 129.15, 129.06, 129.01, 128.55, 127.19, 124.88, 58.99, 17.83, 17.09, 15.47. C26H28N6OS, EI-MS: m/z (M+H+): 473.6 (calculated), 473.4 (found).

1-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl](5-methylthiophen-2-yl)methyl}-4-(2-methylphenyl)piperazine. (5bc). Yield: 85.6%. 1H NMR (400 MHz, CDCl3) δ 7.38 (t, J=7.6 Hz, 1H), 7.30-7.22 (m, 1H), 7.20-7.08 (m, 3H), 7.03-6.89 (m, 2H), 6.69 (d, J=3.5 Hz, 1H), 6.61-6.49 (m, 1H), 4.71 (s, 1H), 3.05-2.73 (m, 6H), 2.68-2.52 (m, 2H), 2.44 (s, 3H), 2.22 (s, 3H), 2.09 (s, 3H), 1.55 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 155.15, 151.33, 142.03, 136.59, 135.97, 133.91, 132.70, 131.82, 131.14, 128.99, 128.97, 128.91, 126.67, 124.76, 123.35, 119.13, 59.37, 51.79, 50.85, 17.97, 17.94, 17.12, 15.51. C26H30N6S, EI-MS: m/z (M+H+): 459.6 (calculated), 459.6 (found).

1-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl](5-methylthiophen-2-yl)methyl}-4-(pyridin-2-yl)piperazine. (5bd). Yield: 73.1%. 1H NMR (400 MHz, CDCl3) δ 8.13 (ddd, J=4.9, 2.0, 1.0 Hz, 1H), 7.49-7.33 (m, 2H), 7.25-7.21 (m, 1H), 7.18-7.12 (m, 1H), 6.69 (d, J=3.5 Hz, 1H), 6.62-6.53 (m, 3H), 4.71 (s, 1H), 3.51 (t, J=5.1 Hz, 4H), 2.86-2.66 (m, 2H), 2.63-2.46 (m, 2H), 2.42 (s, 3H), 2.05 (s, 3H), 1.56 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 154.92, 147.64, 142.10, 137.80, 136.45, 135.96, 133.24, 131.71, 131.17, 129.03, 129.01, 128.96, 124.77, 113.41, 107.27, 59.19, 50.02, 45.35, 17.84, 17.12, 15.45. C24H27N7S, EI-MS: m/z (M+H+): 446.6 (calculated), 446.6 (found).

4-bromo-N-[3-({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl}[4-(pyridin-2-yl)piperazin-1-yl]methyl)phenyl]benzamide. (5be). Yield: 71.3%. 1H NMR (400 MHz, CDCl3) δ 8.23 (d, J=6.0 Hz, 1H), 8.16-8.02 (m, 1H), 7.83-7.66 (m, 3H), 7.65-7.50 (m, 3H), 7.49-7.34 (m, 1H), 7.34-7.16 (m, 4H), 7.16-7.05 (m, 1.5H), 7.01-6.88 (m, 0.5H), 6.68-6.41 (m, 2H), 6.07 (q, J=7.0 Hz, 0.5H), 5.70 (q, J=6.9 Hz, 0.5H), 4.84 (s, 0.5H), 4.78 (s, 0.5H), 3.54-3.43 (m, 2H), 3.43-3.28 (m, 2H), 2.68-2.53 (m, 1H), 2.52-2.27 (m, 3H), 1.94 (d, J=7.0 Hz, 1.5H), 1.88 (d, J=7.0 Hz, 1.5H). 13C NMR (101 MHz, CDCl3) δ 165.12, 165.01, 159.33, 159.30, 154.34, 153.86, 148.00, 147.97, 139.61, 139.18, 138.72, 138.43, 137.64, 137.60, 135.47, 134.72, 133.68, 133.61, 132.07, 132.04, 129.75, 129.40, 129.28, 129.18, 128.93, 128.91, 128.75, 128.72, 126.84, 126.75, 126.58, 126.21, 125.28, 120.94, 120.88, 120.61, 113.68, 113.60, 107.25, 107.16, 64.97, 64.94, 59.01, 58.82, 50.79, 50.72, 45.21, 45.11, 22.82, 22.72. C32H31BrN8O, EI-MS: m/z (M+H+): 624.6 (calculated), 624.6 (found).

1-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl](5-methylthiophen-2-yl)methyl}-4-[3-(trifluoromethyl)pyridin-2-yl]piperazine. (5bf). Yield: 69.3%. 1H NMR (400 MHz, CDCl3) δ 8.40-8.35 (m, 1H), 7.83-7.76 (m, 1H), 7.38 (t, J=7.6 Hz, 1H), 7.27-7.22 (m, 1H), 7.18-7.11 (m, 1H), 6.97-6.89 (m, 1H), 6.74-6.66 (m, 1H), 6.60-6.53 (m, 1H), 4.73 (s, 1H), 3.47-3.08 (m, 4H), 2.91-2.71 (m, 2H), 2.70-2.51 (m, 2H), 2.43 (s, 3H), 2.07 (s, 3H), 1.55 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 159.31, 151.07, 137.37, 137.32, 136.50, 136.03, 131.73, 131.17, 129.03, 128.96, 125.41, 124.82, 116.81, 116.68, 116.37, 59.22, 50.49, 50.32, 17.89, 17.11, 15.49. C25H26F3N7S, EI-MS: m/z (M+H+): 514.6 (calculated), 514.6 (found).

1-(1-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl](5-methylthiophen-2-yl)methyl}piperidin-4-yl)-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bg). Yield: 72.3%. 1H NMR (400 MHz, CDCl3) δ 10.29 (s, 1H), 7.40 (t, J=7.6 Hz, 1H), 7.32-7.27 (m, 1H), 7.21-7.13 (m, 2H), 7.12-7.07 (m, 1H), 7.07-7.00 (m, 2H), 6.77-6.66 (m, 1H), 6.65-6.54 (m, 1H), 4.77 (s, 1H), 4.44-4.17 (m, 1H), 3.35-3.16 (m, 1H), 3.09-2.83 (m, 1H), 2.65-2.32 (m, 6H), 2.32-2.17 (m, 1H), 2.14 (s, 3H), 1.87-1.70 (m, 2H), 1.59 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 155.30, 155.08, 141.94, 136.44, 135.97, 133.57, 131.19, 129.02, 128.21, 124.78, 121.34, 121.11, 109.90, 109.63, 59.01, 51.48, 50.65, 48.84, 29.52, 29.25, 17.89, 17.16, 15.48. C27H29N7OS, EIMS: m/z (M+H+): 500.6 (calculated), 500.4 (found).

1-{1-[(5-bromothiophen-2-yl)({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bh). Yield: 70.1%. 1H NMR (400 MHz, CDCl3) δ 10.53 (s, 1H), 7.48-7.27 (m, 5H), 7.21-6.99 (m, 4H), 6.95 (d, J=3.8 Hz, 0.5H), 6.87 (d, J=3.8 Hz, 0.5H), 6.68 (d, J=3.8 Hz, 0.5H), 6.56 (d, J=3.8 Hz, 0.5H), 6.12 (q, J=7.0 Hz, 0.5H), 5.76 (q, J=7.0 Hz, 0.5H), 5.27 (s, 0.5H), 5.21 (s, 1H), 4.33-4.06 (m, 1H), 3.11-2.90 (m, 1H), 2.90-2.78 (m, 0.5H), 2.73-2.62 (m, 0.5H), 2.59-2.21 (m, 3H), 2.21-1.99 (m, 4H), 1.86-1.56 (m, 2H). 13C NMR (101 MHz, CDCl3) δ 155.33, 155.31, 152.84, 152.74, 139.43, 139.21, 137.96, 137.56, 129.43, 129.34, 129.30, 129.28, 129.12, 129.00, 128.97, 128.84, 128.82, 128.72, 128.26, 128.19, 126.69, 126.27, 121.42, 121.31, 121.06, 120.95, 114.13, 113.82, 110.01, 109.90, 109.51, 109.12, 60.01, 59.26, 58.83, 51.00, 50.51, 50.19, 49.04, 48.55, 29.47, 29.20, 29.04, 22.82, 22.70. C26H26BrN7OS, EI-MS: m/z (M+H+): 565.5 (calculated), 565.3 (found).

1-(1-{[5-(methylsulfanyl)thiophen-2-yl]({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl}piperidin-4-yl)-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bi). Yield: 68.2%. 1H NMR (400 MHz, CDCl3) δ 10.31-10.06 (2S, 1H), 7.55-7.22 (m, 5H), 7.22-6.98 (m, 4H), 6.98-6.63 (m, 2H), 6.17 (q, J=7.0 Hz, 0.5H), 5.72 (q, J=7.0 Hz, 0.5H), 5.21 (2S, 1H), 4.32-4.05 (m, 1H), 3.14-2.85 (m, 1H), 2.85-2.69 (m, 1H), 2.60-1.99 (m, 10H), 1.91-1.53 (m, 2H). 13C NMR (101 MHz, CDCl3) δ 155.25, 153.29, 153.17, 139.63, 139.54, 139.33, 139.20, 138.03, 137.83, 129.91, 129.68, 129.50, 129.30, 129.27, 129.19, 129.09, 128.83, 128.80, 128.73, 128.22, 128.15, 126.74, 126.38, 126.32, 121.44, 121.33, 121.11, 121.04, 109.97, 109.86, 109.63, 109.24, 60.40, 59.53, 59.23, 58.81, 51.44, 50.59, 50.48, 49.25, 48.76, 29.54, 29.26, 29.16, 29.12, 22.85, 21.87, 21.72. C27H29N7OS2, EI-MS: m/z (M+H+): 532.7 (calculated), 532.7 (found).

1-{1-[(1-benzyl-1H-1,2,3,4-tetrazol-5-yl)(thiophen-2-yl)methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bj). Yield: 86.3%. 1H NMR (400 MHz, DMSO-d6) δ 10.79 (s, 1H), 7.66-7.51 (m, 1H), 7.49-7.21 (m, 5H), 7.14-6.86 (m, 6H), 6.01-5.71 (m, 3H), 4.08-3.87 (m, 1H), 3.19-3.01 (m, 1H), 2.99-2.80 (m, 1H), 2.43-2.20 (m, 2H), 2.20-2.01 (m, 2H), 1.72-1.44 (m, 2H). 13C NMR (101 MHz, DMSO-d6) δ 153.67, 153.61, 135.98, 134.81, 129.12, 8.40-8.35 (m, 1H), 7.83-7.76 (m, 1H), 7.38 (t, J=7.6 Hz, 1H), 7.27-7.22 (m, 1H), 7.18-7.11 (m, 1H), 6.97-6.89 (m, 1H), 6.74-6.66 (m, 1H), 6.60-6.53 (m, 1H), 4.73 (s, 1H), 3.47-3.08 (m, 4H), 2.91-2.71 (m, 2H), 2.70-2.51 (m, 2H), 2.43 (s, 3H), 2.07 (s, 3H), 1.55 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 159.31, 151.07, 137.37, 137.32, 136.50, 136.03, 131.73, 131.17, 129.03, 128.96, 125.41, 124.82, 116.81, 116.68, 116.37, 59.22, 50.49, 50.32, 17.89, 17.11, 15.49. C25H26F3N7S, EI-MS: m/z (M+H+): 514.6 (calculated), 514.6 (found).

1-(1-{[1-(2,6-dimethylphenyl)-1H-1,2,3,4-tetrazol-5-yl](5-methylthiophen-2-yl)methyl}piperidin-4-yl)-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bg). Yield: 72.3%. 1H NMR (400 MHz, CDCl3) δ 10.29 (s, 1H), 7.40 (t, J=7.6 Hz, 1H), 7.32-7.27 (m, 1H), 7.21-7.13 (m, 2H), 7.12-7.07 (m, 1H), 7.07-7.00 (m, 2H), 6.77-6.66 (m, 1H), 6.65-6.54 (m, 1H), 4.77 (s, 1H), 4.44-4.17 (m, 1H), 3.35-3.16 (m, 1H), 3.09-2.83 (m, 1H), 2.65-2.32 (m, 6H), 2.32-2.17 (m, 1H), 2.14 (s, 3H), 1.87-1.70 (m, 2H), 1.59 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 155.30, 155.08, 141.94, 136.44, 135.97, 133.57, 131.19, 129.02, 128.21, 124.78, 121.34, 121.11, 109.90, 109.63, 59.01, 51.48, 50.65, 48.84, 29.52, 29.25, 17.89, 17.16, 15.48. C27H29N7OS, EIMS: m/z (M+H+): 500.6 (calculated), 500.4 (found).

1-{1-[(5-bromothiophen-2-yl)({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bh). Yield: 70.1%. 1H NMR (400 MHz, CDCl3) δ 10.53 (s, 1H), 7.48-7.27 (m, 5H), 7.21-6.99 (m, 4H), 6.95 (d, J=3.8 Hz, 0.5H), 6.87 (d, J=3.8 Hz, 0.5H), 6.68 (d, J=3.8 Hz, 0.5H), 6.56 (d, J=3.8 Hz, 0.5H), 6.12 (q, J=7.0 Hz, 0.5H), 5.76 (q, J=7.0 Hz, 0.5H), 5.27 (s, 0.5H), 5.21 (s, 1H), 4.33-4.06 (m, 1H), 3.11-2.90 (m, 1H), 2.90-2.78 (m, 0.5H), 2.73-2.62 (m, 0.5H), 2.59-2.21 (m, 3H), 2.21-1.99 (m, 4H), 1.86-1.56 (m, 2H). 13C NMR (101 MHz, CDCl3) δ 155.33, 155.31, 152.84, 152.74, 139.43, 139.21, 137.96, 137.56, 129.43, 129.34, 129.30, 129.28, 129.12, 129.00, 128.97, 128.84, 128.82, 128.72, 128.26, 128.19, 126.69, 126.27, 121.42, 121.31, 121.06, 120.95, 114.13, 113.82, 110.01, 109.90, 109.51, 109.12, 60.01, 59.26, 58.83, 51.00, 50.51, 50.19, 49.04, 48.55, 29.47, 29.20, 29.04, 22.82, 22.70. C26H26BrN7OS, EI-MS: m/z (M+H+): 565.5 (calculated), 565.3 (found).

1-(1-{[5-(methylsulfanyl)thiophen-2-yl]({1-[(1S)-1-phenylethyl]-1H-1,2,3 ,4-tetrazol-5-yl})methyl}piperidin-4-yl)-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bi). Yield: 68.2%. 1H NMR (400 MHz, CDCl3) δ 10.31-10.06 (2S, 1H), 7.55-7.22 (m, 5H), 7.22-6.98 (m, 4H), 6.98-6.63 (m, 2H), 6.17 (q, J=7.0 Hz, 0.5H), 5.72 (q, J=7.0 Hz, 0.5H), 5.21 (2S, 1H), 4.32-4.05 (m, 1H), 3.14-2.85 (m, 1H), 2.85-2.69 (m, 1H), 2.60-1.99 (m, 10H), 1.91-1.53 (m, 2H). 13C NMR (101 MHz, CDCl3) δ 155.25, 153.29, 153.17, 139.63, 139.54, 139.33, 139.20, 138.03, 137.83, 129.91, 129.68, 129.50, 129.30, 129.27, 129.19, 129.09, 128.83, 128.80, 128.73, 128.22, 128.15, 126.74, 126.38, 126.32, 121.44, 121.33, 121.11, 121.04, 109.97, 109.86, 109.63, 109.24, 60.40, 59.53, 59.23, 58.81, 51.44, 50.59, 50.48, 49.25, 48.76, 29.54, 29.26, 29.16, 29.12, 22.85, 21.87, 21.72. C27H29N7OS2, EI-MS: m/z (M+H+): 532.7 (calculated), 532.7 (found). 1-{1-[(1-benzyl-1H-1,2,3,4-tetrazol-5-yl)(thiophen-2-yl)methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bj). Yield: 86.3%. 1H NMR (400 MHz, DMSO-d6) δ 10.79 (s, 1H), 7.66-7.51 (m, 1H), 7.49-7.21 (m, 5H), 7.14-6.86 (m, 6H), 6.01-5.71 (m, 3H), 4.08-3.87 (m, 1H), 3.19-3.01 (m, 1H), 2.99-2.80 (m, 1H), 2.43-2.20 (m, 2H), 2.20-2.01 (m, 2H), 1.72-1.44 (m, 2H). 13C NMR (101 MHz, DMSO-d6) δ 153.67, 153.61, 135.98, 134.81, 129.12, 128.75, 128.70, 128.22, 128.19, 127.80, 127.11, 126.30, 120.48, 120.24, 108.74, 108.51, 56.83, 50.27, 49.81, 47.61, 28.76, 28.50. C25H25N7OS, EI-MS: m/z (M+H+): 472.6 (calculated), 472.5 (found).

1-{1-[(R)-{1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl}(thiophen-3-yl)methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bk). Yield: 40.3%. The characterization of this compound was reported before (see, Zhang J, et al, Sci Rep 2018;8(1):4653). 1-{1-[(S)-{1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl}(thiophen-3-yl)methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bl). Yield: 36.9%. The characterization of this compound was reported before (see, Zhang J, et al, Sci Rep 2018;8(1):4653).

1-{1-[(1-cyclohexyl-1H-1,2,3,4-tetrazol-5-yl)(thiophen-3-yl)methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bm). Yield: 74.3%. The characterization of this compound was reported before (see, Zhang J, et al, Sci Rep 2018;8(1):4653). 1-{1-[(1-benzyl-1H-1,2,3,4-tetrazol-5-yl)(phenyl)methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bn). Yield: 80.5%. 1H NMR (400 MHz, DMSO-d6) δ 10.80 (s, 1H), 7.52-7.42 (m, 2H), 7.42-7.26 (m, 6H), 7.26-7.17 (m, 2H), 7.13-7.03 (m, 1H), 7.03-6.87 (m, 3H), 5.84 (d, J=3.3 Hz, 2H), 5.42 (s, 1H), 4.07-3.92 (m, 1H), 3.02-2.92 (m, 1H), 2.92-2.76 (m, 1H), 2.36-2.17 (m, 3H), 2.15-1.96 (m, 1H), 1.67-1.46 (m, 2H). 13C NMR (101 MHz, DMSO-d6) δ 154.39, 153.64, 134.69, 134.64, 129.20, 129.13, 128.72, 128.26, 128.23, 128.17, 127.72, 120.48, 120.29, 108.74, 108.60, 79.16, 61.98, 50.20, 49.93, 49.88, 49.01, 28.72, 28.56. C27H27N7O, EI-MS: m/z (M+H+): 466.6 (calculated), 466.6 (found).

1-{1-[(1-benzyl-1H-1,2,3,4-tetrazol-5-yl)(2-methylphenyl)methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bo). 1H NMR (400 MHz, CDCl3) δ 10.21 (s, 1H), 7.39-6.98 (m, 13H), 5.78-5.50 (m, 1H), 5.36-5.04 (m, 2H), 4.41-4.19 (m, 1H), 2.99-2.77 (m, 1H), 2.77-2.56 (m, 2H), 2.54-2.29 (m, 5H), 2.29-2.08 (m, 1H), 1.84-1.58 (m, 2H). 13C NMR (101 MHz, CDCl3) δ 155.25, 154.11, 137.74, 133.33, 131.57, 129.16, 128.93, 128.68, 128.21, 127.43, 126.26, 121.36, 121.06, 109.92, 109.43, 60.92, 51.31, 51.16, 50.95, 49.06, 29.49, 19.48. C28H29N7O, EI-MS: m/z (M+H+): 480.6 (calculated), 480.6 (found).

1-{1-[phenyl({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bp). Yield: 71.3%. 1H NMR (400 MHz, CDCl3) δ 10.27 (s, 0.5H), 10.22 (s, 0.5H), 7.48-6.92 (m, 1H), 6.03 (q, J=7.0 Hz, 0.5H), 5.52 (q, J=7.0 Hz, 0.5H), 4.99 (s, 0.5H), 4.83 (s, 0.5H), 4.36-4.08 (m, 1H), 3.24-3.06 (m, 0.5H), 2.97-2.75 (m, 1H), 2.71-2.62 (m, 0.5H), 2.60-2.21 (m, 3H), 2.21-2.01 (m, 1H), 1.99-1.83 (m, 3H), 1.83-1.60 (m, 2H). 13C NMR (101 MHz, CDCl3) δ 155.32, 154.50, 154.06, 139.55, 139.17, 134.59, 134.34, 129.29, 129.21, 129.17, 129.09, 129.00, 128.97, 128.80, 128.74, 128.67, 128.22, 128.13, 126.60, 126.22, 121.44, 121.34, 121.11, 110.00, 109.87, 109.75, 109.40, 64.86, 64.74, 58.79, 58.60, 51.54, 50.85, 50.75, 50.66, 50.50, 50.16, 29.42, 29.24, 29.05, 22.67, 22.61. C28H29N7O, EI-MS: m/z (M+H+): 480.6 (calculated), 480.4 (found).

1-{1-[(2-methylphenyl)({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bq). Yield: 87.3%. 1H NMR (400 MHz, DMSO d6) δ 10.81 (2S, 1H), 7.45-7.29 (m, 1H), 7.29-7.09 (m, 8H), 7.09-6.85 (m, 4H), 6.19 (q, J=6.8 Hz, 0.5H), 5.91 (q, J=6.8 Hz, 0.5H), 5.53 (s, 0.5H), 5.41 (s, 0.5H), 4.19-3.97 (m, 1H), 3.16-2.99 (m, 0.5H), 2.74-1.99 (m, 8.5H), 1.79 (dd, J=6.9, 2.7 Hz, 3H), 1.72-1.43 (m, 2H). 13C NMR (101 MHz, DMSO-d6) δ 153.64, 153.61, 153.53, 153.28, 139.59, 139.26, 137.43, 137.13, 133.64, 133.61, 131.07, 130.84, 129.14, 129.12, 128.80, 128.62, 128.50, 128.41, 128.28, 128.24, 128.21, 128.14, 127.96, 127.86, 126.34, 126.17, 125.78, 125.58, 120.50, 120.47, 120.30, 108.77, 108.64, 108.52, 59.24, 59.18, 57.23, 50.39, 50.09, 50.02, 48.23, 48.03, 28.88, 28.70, 22.43, 22.08, 19.14, 18.98. C29H31N7O, EI-MS: m/z (M+H+): 494.6 (calculated), 494.6 (found).

1-[1-({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl}(1,2,3-thiadiazol-4-yl)methyl)piperidin-4-yl]-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5br). Yield: 72.6%. 1H NMR (400 MHz, CDCl3) δ 10.28 (s, 0.7H), 10.25 (s, 0.3H), 9.28 (s, 0.7H), 9.13 (s, 0.3H), 7.56-7.28 (m, 5H), 7.13-6.95 (m, 3.4H), 6.87-6.77 (m, 0.6H), 6.45 (q, J=7.0 Hz, 0.3H), 6.14 (s, 0.7H), 6.04 (q, J=7.0 Hz, 0.7H), 5.86 (s, 0.3H), 4.18-3.95 (m, 1H), 3.25-3.06 (m, 1H), 2.87-2.63 (m, 1H), 2.54-1.65 (m, 9H). 13C NMR (101 MHz, CDCl3) δ 155.23, 155.16, 152.43, 152.38, 139.55, 139.29, 137.99, 137.84, 129.41, 129.22, 129.16, 128.92, 128.76, 128.20, 128.12, 126.57, 126.38, 121.50, 121.39, 121.12, 120.92, 110.00, 109.90, 109.50, 108.97, 59.55, 58.92, 57.82, 56.98, 52.43, 52.06, 50.47, 50.31, 47.58, 46.80, 29.46, 29.39, 29.08, 28.67, 22.99, 22.78. C24H25N9OS, EI-MS: m/z (M+H+): 488.6 (calculated), 488.5 (found).

1-{1-[(2,1,3-benzoxadiazol-5-yl)({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bs). Yield: 69.8%. 1H NMR (400 MHz, DMSO-d6) δ 10.80 (2S, 1H), 8.22-8.03 (m, 1H), 8.02-7.82 (m, 1H), 7.70-7.57 (m, 0.5H), 7.52-7.46 (m, 0.5H), 7.47-7.28 (m, 2.5H), 7.27-7.05 (m, 3H), 7.02-6.91 (m, 3.5H), 6.32 (qd, J=7.0, 1.8 Hz, 1H), 5.63 (2S, 1H), 4.22-4.04 (m, 0.5H), 4.03-3.83 (m, 0.5H), 3.17-3.03 (m, 0.5H), 2.98-2.79 (m, 1H), 2.79-2.66 (m, 0.5H), 2.50-2.31 (m, 2H), 2.31-2.16 (m, 1H), 2.16-1.80 (m, 4H), 1.73-1.32 (m, 2H). 13C NMR (101 MHz, DMSO-d6) δ 153.67, 153.57, 152.71, 152.67, 148.70, 148.49, 148.35, 148.27, 140.02, 139.89, 139.81, 139.53, 134.04, 133.25, 129.23, 129.03, 128.80, 128.62, 128.27, 128.20, 128.12, 127.95, 126.43, 126.18, 120.50, 120.33, 120.23, 116.11, 115.79, 115.54, 108.75, 108.60, 108.52, 61.48, 61.24, 57.34, 57.20, 49.84, 49.74, 49.63, 49.26, 48.94, 28.74, 28.49, 22.40, 22.10. C28H27N9O2, EIMS: m/z (M+H+): 522.6 (calculated), 522.6 (found).

1-{1-[(1-benzothiophen-2-yl)({1-[(1S)-1-phenylethyl]-1H-1,2,3,4-tetrazol-5-yl})methyl]piperidin-4-yl}-2,3-dihydro-1H-1,3-benzodiazol-2-one. (5bt). Yield: 72.3%. 1H NMR (400 MHz, CDCl3) δ 10.03 (2S, 1H), 7.54-7.22 (m, 7.5H), 7.22-7.00 (m, 5H), 7.00-6.85 (m, 1.5H), 6.22 (q, J=7.0 Hz, 0.5H), 5.67 (q, J=7.0 Hz, 0.5H), 5.31 (s, 0.5H), 5.27 (s, 0.5H), 4.33-4.10 (m, 1H), 3.14-3.00 (m, 0.5H), 3.00-2.88 (m, 0.5H), 2.88-2.71 (m, 1H), 2.64-2.31 (m, 2H), 2.31-2.12 (m, 1H), 2.12-1.98 (m, 3H), 1.90-1.54 (m, 3H). 13C NMR (101 MHz, CDCl3) δ 155.18, 153.73, 153.54, 139.59, 139.37, 136.35, 136.13, 129.32, 129.25, 129.13, 128.84, 128.81, 128.77, 128.50, 128.19, 128.11, 127.02, 126.84, 126.75, 126.67, 126.45, 126.34, 121.44, 121.33, 121.12, 121.07, 109.94, 109.82, 109.70, 109.28, 60.19, 59.25, 59.19, 58.78, 51.59, 50.63, 50.55, 49.35, 48.77, 29.56, 29.26, 29.15, 22.87, 22.80. C30H29N7OS, EIMS: m/z (M+H+): 536.7 (calculated), 536.5 (found).

Example III

This example describes the materials and methods implemented during the experiments described in Examples I and II.

Animals.

Pathogen-free, adult male and female Sprague-Dawley rats (225-250g; Envigo, Indianapolis, Ind.) were housed in temperature-controlled (23±3 ° C.) and light-controlled (12-h light/12-h dark cycle; lights on 07:00-19:00) rooms with standard rodent chow and water available ad libitum. The Institutional Animal Care and Use Committee of the College of Medicine at the University of Arizona approved all experiments. All procedures were conducted in accordance with the Guide for Care and Use of Laboratory Animals published by the National Institutes of Health and the ethical guidelines of the International Association for the Study of Pain. Animals were randomly assigned to treatment or control groups for the behavioral experiments. Animals were initially housed 3 per cage but individually housed after the intrathecal cannulation. All behavioral experiments were performed by experimenters who were blinded to the experimental groups and treatments.

Preparation of Acutely Dissociated Dorsal Root Ganglion Neurons

Dorsal root ganglia from all levels were acutely dissociated using methods as described previously [23]. Rat DRG neurons were isolated from 100g female Sprague-Dawley rats using previously developed procedures [53]. In brief, removing dorsal skin and muscle and cutting the vertebral bone processes parallel to the dissection stage exposed the DRGs. DRGs were then collected, trimmed at their roots, and enzymatically digested in 3 mL bicarbonate-free, serum-free, sterile DMEM (Cat# 11965, Thermo Fisher Scientific, Waltham, Mass.) solution containing neutral protease (3.125 mg.ml-1, Cat#LS02104; Worthington, Lakewood, N.J.) and collagenase type I (5 mg/mL, Cat# LS004194, Worthington, Lakewood, N.J.) and incubated for 60 minutes at 37° C. under gentle agitation. Dissociated DRG neurons (˜1.5×10⁶) were then gently centrifuged to collect cells and washed with DRG media DMEM containing 1% penicillin/streptomycin sulfate from 10,000 μg/mL stock, 30 ng/mL nerve growth factor, and 10% fetal bovine serum before plating onto poly-D-lysine- and laminin-coated glass 12- or 15-mm coverslips.

Calcium Imaging in Acutely Dissociated Dorsal Root Ganglion Neurons

Dorsal root ganglion neurons were loaded for 30 minutes at 37° C. with 3 μM Fura-2AM (Cat# F1221, Thermo Fisher, stock solution prepared at 1 mM in DMSO, 0.02% pluronic acid, Cat#P-3000MP, Thermo Fisher) to follow changes in intracellular calcium([Ca2+]c) in a standard bath solution containing 139 mM NaCl, 3 mM KCl, 0.8 mM MgCl2, 1.8 mM CaCl2, 10 mM Na HEPES, pH 7.4, 5 mM glucose exactly as previously described [7] Fluorescence imaging was performed with an inverted microscope, NikonEclipseTi-U (Nikon Instruments Inc., Melville, N.Y.), using objective Nikon Fluor 4X and a Photometrics cooled CCD camera CoolSNAPES2 (Roper Scientific, Tucson, Ariz.) controlled by NIS Elements software (version 4.20, Nikon Instruments).The excitation light was delivered by a Lambda-LS system (Sutter Instruments, Novato, Calif.). The excitation filters (340±5 and 380±7) were controlled by a Lambda 10 to 2 optical filter change (Sutter Instruments). Fluorescence was recorded through a 505-nm dichroic mirror at 535±25 nm. To minimize photobleaching and phototoxicity, the images were taken every ˜10 seconds during the time-course of the experiment using the minimal exposure time that provided acceptable image quality. The changes in [Ca2+]c were monitored by following a ratio of F₃₄₀/F₃₈₀, calculated after subtracting the background from both channels.

Dorsal Root Ganglia Neuron Transfection.

Collected cells were re-suspended in Nucleofector transfection reagent containing siRNA at 500 nM and 2 μg of the provided GFP plasmid as detailed previously [17]. Cells were then subjected to electroporation protocol O-003 in an Amaxa Biosystem (Lonza, Basel, Switzerland) and plated onto poly-D-lysine- and laminin-coated glass 12-mm coverslips. Transfection efficiencies were routinely between 20% and 30% with ˜10% cell death. Small diameter neurons were selected to target Aδ- and c-fiber nociceptive neurons. For rat DRG culture small cells were considered to be ˜<30 μm as determined by an eyepiece micrometer within the objective lens. Successfully transfected cells were identified by GFP fluorescence. The siRNA sequences used were: UAGAUAGCAAAUACUUUGGCCGGGG (SEQ ID NO: 1) (for Cacna1g/CaV3.1; (Cat# RSS355855, Thermofisher)); CAGCCAUCUUCGUGGUGGAGAUGAU (SEQ ID NO: 2) (for Cacna1h/CaV3.2; (Cat# RSS350286, Thermofisher)); CAGCAUCCUUGGGAUGCAUAUCUUU (SEQ ID NO: 3) (for Cacna1i/CaV3.3; Cat# RSS367566); and siRNA Negative Control, Med GC was used as a scrambled siRNA control (Cat# 12935300). Cells were used 48 hrs after transfection.

Constellation Pharmacology.

These experiments were performed as described previously [53; 76], but with the following modifications. Dorsal root ganglia neurons were loaded at 37° C. with 3 μM Fura-2AM for 30 minutes in Tyrode solution (at ˜310 mOsm) containing 119 mM NaCl, 2.5 mM KCl, 2 mM MgCl₂, 2 mM CaCl2, 25 mM HEPES, pH 7.4, and 30 mM glucose. After a 1-minute baseline measurement, Ca²⁺ influx was stimulated by the addition of the following receptor agonists: 400 nM menthol, 50 μM histamine, 10 μM adenosine triphosphate (ATP), 200 μM allyl isothiocyanate (AITC), 1 mM acetylcholine (Ach), and 100 nM capsaicin diluted in Tyrode solution. At the end of the constellation pharmacology protocol, cell viability was assessed by depolarization-induced Ca²⁺ influx using and an excitatory KCl solution comprising 32 mM NaCl, 90 mM KCl, 2 mM MgCl₂, 2 mM CaCl₂, 25 mM HEPES, pH 7.4, and 30 mM glucose. After the 1-minute baseline measurement, each trigger was applied for 15 seconds in the order indicated above in 6-minute intervals. After each trigger, bath solution was continuously perfused over the cells to wash off excess of the trigger. This process was automated using the ValveBank II perfusion system that controlled the perfusion of the standard bath solution and triggers (Automate Scientific, San Diego, Calif.). Except for the time course experiments, 5bk was incubated overnight onto DRGs. In all cases, 5bk was also added to the Tyrode solution during the loading with Fura-2AM. Fluorescence imaging was performed under the same conditions noted above for calcium imaging. A cell was defined as a “responder” if its fluorescence ratio of 340 nm/380 nm was greater than 10% of the baseline value calculated using the average fluorescence in the 30 seconds preceding application of the trigger.

Whole-Cell Patch Recordings of Ca2⁺ and Na2⁺ Currents in Acutely Dissociated DRG Neurons.

Recordings were obtained from acutely dissociated DRG neurons as described previously [34; 54]. To isolate calcium currents, Na⁺ and K⁺ currents were blocked with 500 nM tetrodotoxin (TTX; Alomone Laboratories) and 30 mM tetraethylammonium chloride (TEA-Cl; Sigma). Extracellular recording solution (at ˜310 mOsm) consisted of the following (in mM): 110 N-methyl-D-glucamine (NMDG), 10 BaCl₂, 30 TEA-Cl, 10 HEPES, 10 glucose, pH at 7.4, 0.001 TTX, 0.01 nifedipine. The intracellular recording solution (at ˜310 mOsm) consisted of the following (in mM): 150 CsCl₂, 10 HEPES, 5 Mg-ATP, 5 BAPTA, pH at 7.4. The protocol for isolating T-type calcium currents was previously described by Choe et al.[14] The extracellular recording solution used to isolate T currents consisted of the following (in millimolar): 2 CaCl₂, 152 TEA-Cl, 10 HEPES, pH adjusted to 7.4 with TEA-OH. The intracellular recording solution consisted of (in millimolar): 135 tetramethylammonium hydroxide, 10 EGTA, 40 HEPES, and 2 MgCl₂, pH adjusted to 7.2 with hydrofluoric acid. Activation of I_(Ca-T) was measured by using a holding voltage of −90 mV with voltage steps 200 ms in duration applied at 500-ms intervals in 10 mV increments from −70 to +60 mV. Inactivation of I_(Ca-T) was determined by applying a 1500-ms conditioning prepulse (−110 to+20 mV in 10 mV increments) after which the voltage was stepped to −30 mV for 20 ms; a 40-ms interval with a holding voltage of −90 mV separated each acquisition. In the deactivation tau protocol, the neuron was first held at −110 mV, then the voltage jumped to −30 mV for 10 ms followed by a 50-ms conditioning prepulse (−160 to −40 mV in 10 mV increments). A 2-second interval with a holding voltage of −90 mV separated each acquisition. I_(Ca-T) recovery from inactivation were obtained by using our standard double-pulse protocol with variable interpulse duration at −90 mV after a 500-ms-long inactivating pulse (V_(h)=−90 mV; V_(t)=−30 mV).

To isolate the contributions of the HVA calcium channel subtypes, we applied all but one of the following subunit-selective blockers (all purchased from Alomone Labs, Jerusalem): Nifedipine (10 μM, L-type); ω-agatoxin GIVA (200 nM, P/Q-type) [52]; SNX-482 (200 nM, R-type) [56]; ω-conotoxin GVIA (500 nM, N-type) [30] or TTA-P2 (1 μM, T-type)[14] to individually isolate the subtypes.

For recording sodium currents the internal solution consisted of (in mM): 140 CsF, 10 NaCl, 1.1Cs-EGTA, and 15 HEPES (pH 7.3, mOsm/L=290-310) and external solution contained (in mM): 140 NaCl, 30 tetraethylammonium chloride, 10 D-glucose, 3 KCl, 1 CaCl₂, 0.5 CdCl₂, 1 MgCl₂, and 10 HEPES (pH 7.3, mOsm/L=310-315). DRG neurons were interrogated with current-voltage (I-V) and activation/inactivation voltage protocols as previously described [17; 23]. The voltage protocols were as follows: (a) I-V protocol: from a −60 mV holding potential, cells were depolarized in 150-millisecond voltage steps from −70 to +60 mV (5-mV increments) which permitted acquisition of current density values such that we could analyze activation of sodium channels as a function of current vs voltage and infer peak current density (normalized to cell capacitance (in picofarads, pF)), which occurred between ˜0 to 10 mV; (b) inactivation protocol: from a −60 mV holding potential, cells were subjected to hyperpolarizing/repolarizing pulses for 1 second between −120 to 0 mV (+10 mV steps). This increment conditioned various proportions of channels into a state of fast-inactivation—in this case 0-mV test pulse for 200 milliseconds was able to reveal fast inactivation when normalized to maximum sodium current. Because of the differential inactivation kinetics of TTX-resistant and TTX-sensitive channels, the fast inactivation protocol allowed subtraction of electrically isolated TTX-R (current available after −40mV prepulse) from total current (current available after −120mV prepulse), as previously described [17]. Pipettes with 1 to 3 MΩ resistance were used for all recordings.

The Boltzmann relation was used to determine the voltage dependence for activation of I_(Ca) and I_(Na) wherein the conductance-voltage curve was fit by the equation G/G_(max)=1/[1+exp (V_(0.5)−V_(m))/k], where G is the conductance G=I/(V_(m)-E_(Ca) or E_(Na)), G_(max) is the maximal conductance obtained from the Boltzmann fit under control conditions, V_(0.5) is the voltage for half-maximal activation, V_(m) is the membrane potential, and k is a slope factor. E_(Ca) is the reversal potential for I_(Ca); E_(Na) is the reversal potential for I_(Na) and was determined for each individual neuron. The values of I_(Ca) and I_(Na) around the reversal potential were fit with a linear regression line to establish the voltage at which the current was zero. The Boltzmann parameters were determined for each individual neuron and then used to calculate the mean±SEM.

Whole-cell recordings were obtained with a HEKA EPC-10 USB (HEKA Instruments Inc.); data were acquired with a Patchmaster (HEKA) and analyzed with a Fitmaster (HEKA). Capacitive artifacts were fully compensated, and series resistance was compensated by ˜70%. Recordings made from cells with greater than a 5-mV shift in series resistance compensation error were excluded from analysis. All experiments were performed at room temperature (˜23° C.). Pipettes with 1-3MΩ resistance were used for all recordings.

Calcitonin Gene-Related Peptide Release from Lumbar Slices.

Rats were deeply anesthetized with 5% isofluorane and then decapitated. Two vertebral incisions (cervical and lumbar) were made in order to expose the spinal cord. Pressure was applied to a saline-filled syringe inserted into the lumbar vertebral foramen, and the spinal cord was extracted. Only the lumbar region of the spinal cord was used for the CGRP release assay. Baseline treatments (#1 and #2) involved bathing the spinal cord in Tyrode's solution. The excitatory solution consisting of 90 mM KCl was paired with the treatment for fraction #4. These fractions (10 minutes, 400 μL each) were collected for measurement of CGRP release. Samples were immediately flash frozen and stored in a −20° C. freezer. 5bk (20 μM) or vehicle (0.9% saline) was added to the pretreatment and cotreatment fractions (#3 and 4). The concentration of CGRP released into the buffer was measured by enzyme-linked immunosorbant assay (Cat# 589001, Cayman Chemical, Ann Arbor, Mich.).

Preparation of Spinal Cord Slices.

As described previously [90], young rats (postnatal 10-14 days) were deeply anesthetized with diethyl ether. For spinal nerve blocking, 0.3 mL of 2% lidocaine was injected to both sides of L4 to 5 lumbar vertebrae. Laminectomy was performed from mid-thoracic to low lumbar levels, and the spinal cord was quickly removed to cold modified artificial cerebrospinal fluid (aCSF) oxygenated with 95% O₂ and 5% CO₂. The aCSF contained (in millimolar): 80 NaCl, 2.5 KCl, 1.25 NaH₂PO₄, 0.5 CaCl₂, 3.5 MgCl₂, 25 NaHCO₃, 75 sucrose, 1.3 ascorbate, 3.0 sodium pyruvate, with pH at 7.4 and osmolarity at 310 mOsm. Transverse 350-μm thick slices were obtained by a vibratome (VT1200S; Leica, Nussloch, Germany). Slices were then incubated for at least 1 hour at RT in an oxygenated recording solution containing (in millimolar): 125 NaCl, 2.5 KCl, 2 CaCl₂, 1 MgCl₂, 1.25 NaH₂PO₄, 26 NaHCO₃, 25 D-glucose, 1.3 ascorbate, 3.0 sodium pyruvate, with pH at 7.4 and osmolarity at 320 mOsm. The slices were then positioned in a recording chamber and continuously perfused with oxygenated recording solution at a rate of 3 to 4 mL/min before electrophysiological recordings at RT.

Electrophysiological Recording in Spinal Cord Slices by Whole-Cell Patch Clamp.

Substantia gelatinosa neurons were visualized and identified in the slices by means of infrared differential interference contrast video microscopy on an upright microscope (FN1; Nikon, Tokyo, Japan) equipped with a 3 40/0.80 water-immersion objective and a charge-coupled device camera. Patch pipettes with resistance at 6 to 10 MΩ were made from borosilicate glass (Sutter Instruments, Novato, Calif.) on a 4-steps micropipette puller (P-90; Sutter Instruments, Novato, Calif.). The pipette solution contained the following (in millimolar): 120 potassium gluconate, 20 KCl, 2 MgCl 2, 2 Na 2-ATP, 0.5 Na-GTP, 20 HEPES, 0.5 EGTA, with pH at 7.28 and osmolarity at 310 mOsm. The membrane potential was held at −60 mV using PATCHMASTER software in combination with a patch clamp amplifier (EPC10; HEKA Elektronik, Lambrecht, Germany).

The whole-cell configuration was obtained in voltage-clamp mode. To record spontaneous excitatory postsynaptic currents (sEPSCs), bicuculline methiodide (10 m M) and strychnine (1 m M) were added to the recording solution to block γ-aminobutyric acid-activated and glycine-activated currents. Hyperpolarizing step pulses (5 mV in intensity, 50 milliseconds in duration) were periodically delivered to monitor the access resistance (15-25 MΩ), and recordings were discontinued if the access resistance changed by more than 20%. For each neuron, sEPSCs were recorded for a total duration of 2 minutes. Currents were filtered at 3 kHz and digitized at 5 kHz. Data were further analyzed by the Mini-Analysis (Synatosoft Inc, N.J.) and Clampfit 10.7 Program. The amplitude and frequency of sEPSCs were compared between neurons from animals in control and 5bk groups.

Implantation of Intrathecal Catheter.

For intrathecal (i.t.) drug administration, rats were chronically implanted with catheters as described by Yaksh and Rudy [89]. Rats were anesthetized with ketamine/xylazine and placed in a stereotactic head holder. The occipital muscles were separated from their occipital insertion and retracted caudally to expose the cisternal membrane at the base of the skull. Polyethylene tubing was passed caudally from the cisterna magna to the level of the lumbar enlargement. Animals were allowed to recover and were examined for evidence of neurologic injury. Animals with evidence of neuromuscular deficits were excluded.

Testing of Allodynia.

The assessment of tactile allodynia (i.e., a decreased threshold to paw withdrawal after probing with normally innocuous mechanical stimuli) consisted of testing the withdrawal threshold of the paw in response to probing with a series of calibrated fine (von Frey) filaments. Each filament was applied perpendicularly to the plantar surface of the paw of rats held in suspended wire mesh cages. Withdrawal threshold was determined by sequentially increasing and decreasing the stimulus strength (the “up and down” method), and data were analyzed with the nonparametric method of Dixon, as described by Chaplan et al [11] and expressed as the mean withdrawal threshold.

HIV Sensory Neuropathy (HIV SIV).

Mechanical allodynia was produced by intrathecal administration of the human immunodeficiency virus-1 (HIV-1) envelope glycoprotein, GP120 [51]. Seven days after implantation of an intrathecal catheter, baseline behavioral measurements were obtained and then rats were randomly assigned to two groups. On days 10, 12 and 14, rats were injected i.t. with 300 ng of GP120 (Cat#4961, HIV-1 BaL gp120 recombinant protein, NIH-AIDS Reagent program) in a final volume of 20 μl in 0.9% saline and 0.1% BSA. Rats were tested on day 35 (i.e., 21 days after the last i.t. injection of GP120).

Paclitaxel-Induced Neuropathy Model.

Rats were given paclitaxel (Cat# P-925-1, Goldbio, Olivette, Mo.) based on the protocol described by Polomano et al. [60]. In brief, pharmaceutical-grade paclitaxel (Taxol) was resuspended at a concentration of 2 mg/ml in 30% 1:1 Cremophor EL: ethanol, 70% Saline and given to the rats at 2 mg/kg intraperitoneally (i.p.) every other day for a total of 4 injections (days 0, 2, 4, and 6), resulting in a final cumulative dose of 8 mg/kg. No abnormal spontaneous behavioral changes in the rats were noted during or after the treatment. Animals developed mechanical hyperalgesia within 10 days after the first paclitaxel injection.

Elevated Plus Maze (EPM).

The EPM consists of four elevated (50 cm) arms (50 cm long and 10 cm wide) with two opposing arms containing 30 cm high opaque walls. EPM testing occurred in a quiet testing room with ambient lighting at ˜500 lux. On day of testing, rats were allowed to acclimate to the testing room for 20 minutes. Each rat was placed in a closed arm, facing the enter platform and cage mates started in the same closed arm. Each rat was allowed 5 minutes to explore the EPM and then returned to its home cage. Between animals the EPM was cleaned thoroughly with Versa-Clean (Fisher Scientific). EPM performance was recorded using an overhead video camera (MHD Sport 2.0 WiFi Action Camera, Walmart.com) for later quantification. Open and closed arm entries were defined as the front two paws entering the arm, and open arm time began the moment the front paws entered the open arm and ended upon exit. An anxiety index was also calculated; the index combines EPM parameters into one unified ratio with values ranging from 0 to 1, with a higher value indicating increased anxiety [33]. The following equation was used for calculation of the anxiety index: Anxiety Index=1−(open arm time/5 min)+(open arm entry/total entry)

Spinal Nerve Ligation (SNL).

Nerve ligation, performed as described earlier [40; 53], produces signs of neuropathic dysesthesias, including tactile allodynia and thermal hypersensitivity. All nerve operations occurred 5 days after intrathecal catheter implantation. Rats were anesthetized with 2% isoflurane in O₂ anesthesia delivered at 2 L/min. The skin over the caudal lumbar region was incised and the muscles retracted. The L₅ and L₆ spinal nerves were exposed, carefully isolated, and tightly ligated with 4-0 silk distal to the dorsal root ganglion without limiting the use of the left hind paw of the animal. All animals were allowed 7 days to recover before any behavioral testing. Any animals exhibiting signs of motor deficiency were euthanized.

Rotarod.

Rats were trained to walk on a rotating rod (10 rev/min; Rotamex 4/8 device) with a maximal cutoff time of 180 seconds. Training was initiated by placing the rats on a rotating rod and allowing them to walk until either falling off, or maximal cutoff time was reached. This process was repeated 6 times and the rats were allowed to recover for 24 hours before intrathecal compound administration. Prior to treatment, the rats were run once on a moving rod in order to establish a baseline value. Assessment consisted of placing the rats on the moving rod and timing until either they fell off or reached a maximum of 180 seconds.

Competition Radioligand Binding

Details on our cell lines, culture methods, and binding methods have been reported previously [59]. All cells were Chinese Hamster Ovary (CHO-K1) cells overexpressing human opioid receptor (mu [MOR], delta [DOR], or kappa [KOR]). Cell pellets for binding were prepared by growing cells to confluency in 15 cm dishes, 3 per pellet. The cells were collected using 5 mM EDTA in dPBS (no trypsin) and stored at −80° C. until the assay was performed. The assay was performed by incubating 18.5-25 μg of membrane protein with 0.97-4.76 nM of ³H-diprenorphine (PerkinElmer) and concentration curves of 5bk or positive control (naloxone for MOR and DOR, U50,488 for KOR) in a 200 μL volume for 1 hour at room temperature. Reactions were harvested using a 96 well format Brandel Cell Harvester, and data acquired using a PerkinElmer MicroBeta2 6-detector 96-well format scintillation counter. The data was normalized to binding in the presence of Vehicle (100%; 0.1% DMSO and 0.1% BSA) and non-specific binding (0%; 10 μM naloxone) and reported as the mean±SEM. Curves were fit using a 1-site binding 3-variable nonlinear regression model with GraphPad Prism 8.3, using the previously-measured K_(D) values of ³H-diprenorphine in these cells [59]. The data output was reported as the mean Ki±SEM of N=3 independent experiments.

Statistical Analysis.

All data was first tested for a Gaussian distribution using a D'Agostino-Pearson test (Prism 8 Software, Graphpad, San Diego, Calif.). SNI-(day 15 post-surgery), GP120-(day 15 post last injection) and paclitaxel-(day 15 post-injection) induced allodynia was quantified as percentage of maximum possible allodynia using the formula: percentage allodynia=[(baseline threshold−post-injury threshold)/baseline threshold]×100. Reversal of allodynia by drugs (that is, anti-allodynia) was quantified with respect to the area under the threshold-time curve (using the trapezoidal method) over the post-injection testing period. Data are reported as percentage of the maximum possible anti-allodynia, calculated for each rat as a ratio of its actual anti-allodynia compared to a hypothetical situation in which the drug brought withdrawal thresholds to their original baseline at all post-injection time points. The statistical significance of differences between means was determined by a parametric ANOVA followed by Tukey's post hoc or a non-parametric Kruskal Wallis test followed by Dunn's post-hoc test depending on if datasets achieved normality. Behavioral data with a time course were analyzed by Two-way ANOVA with Sidak's post hoc test. Differences were considered significant if p≤0.05. Error bars in the graphs represent mean±SEM. See statistical analysis described in Table 1. All data were plotted in Prism 8. No outlier data were removed.

TABLE 1 Statistical analyses of experiments. Figure Statistical test; Post-hoc analysis Number of Number of subjects panel Assay findings (adjusted p-values) subjects excluded (ROUT test) FIG. 3A Calcium imaging - One-way ANOVA Dunnett’s multiple comparisons test DMSO 0.01% screening with a 40 mM p < 0.0001 DMSO 0.01% vs. 5aa < 0.0001 n = 1032 KCl challenge DMSO 0.01% vs. 5ab < 0.0001 5aa n = 378 DMSO 0.01% vs. 5ac 0.9988 5ab n = 995 DMSO 0.01% vs. 5ad 0.0023 5ac n = 471 DMSO 0.01% vs. 5ae < 0.0001 5ad n = 200 DMSO 0.01% vs. 5af < 0.0001 5ae n = 554 DMSO 0.01% vs. 5ag < 0.0001 5af n=244 DMSO 0.01% vs. 5ah < 0.0001 5ag n = 242 DMSO 0.01% vs. 5ai < 0.0001 5ah n=275 DMSO 0.01% vs. 5aj 0.9998 5ai n = 542 DMSO 0.01% vs. 5ak 0.014 5aj n = 409 DMSO 0.01% vs. 5al 0.5522 5ak n=214 DMSO 0.01% vs. 5am < 0.0001 5al n = 590 DMSO 0.01% vs. 5an 0.0012 5am n = 216 DMSO 0.01% vs. 5ao < 0.0001 5an n = 437 DMSO 0.01% vs. 5ap < 0.0001 5ao n = 567 DMSO 0.01% vs. 5aq < 0.0001 5ap n = 222 DMSO 0.01% vs. 5ar < 0.0001 5aq n = 683 DMSO 0.01% vs. 5as < 0.0001 5ar n = 455 DMSO 0.01% vs. 5at < 0.0001 5as n = 357 DMSO 0.01% vs. 5au < 0.0001 5at n = 934 DMSO 0.01% vs. 5av < 0.0001 5au n = 885 DMSO 0.01% vs. 5aw < 0.0001 5av n = 534 DMSO 0.01% vs. 5ax < 0.0001 5aw n = 264 DMSO 0.01% vs. 5ay < 0.0001 5ax n = 597 DMSO 0.01% vs. 5az 0.9264 5ay n = 852 DMSO 0.01% vs. 5ba < 0.0001 5az n = 1132 DMSO 0.01% vs. 5bb < 0.0001 5ba n = 802 DMSO 0.01% vs. 5bc < 0.0001 5bb n = 567 DMSO 0.01% vs. 5bd < 0.0001 5bc n = 530 DMSO 0.01% vs. 5be 0.9987 5bd n = 751 DMSO 0.01% vs. 5bf 0.9988 5be n = 348 DMSO 0.01% vs. 5bg < 0.0001 5bf n = 284 DMSO 0.01% vs. 5bh < 0.0001 5bg n = 747 DMSO 0.01% vs. 5bi < 0.0001 5bh n = 802 DMSO 0.01% vs. 5bj 0.767 5bi n = 644 DMSO 0.01% vs. 5bk < 0.0001 5bj n = 95 DMSO 0.01% vs. 5bl < 0.0001 5bk n = 78 DMSO 0.01% vs. 5bm < 0.0001 5bl n = 958 DMSO 0.01% vs. 5bn 0.9994 5bm n = 381 DMSO 0.01% vs. 5bo < 0.0001 5bnn = 100 DMSO 0.01% vs. 5bp < 0.0001 5bo n = 559 DMSO 0.01% vs. 5bq < 0.0001 5bp n = 604 DMSO 0.01% vs. 5br < 0.0001 5bq n = 681 DMSO 0.01% vs. 5bs < 0.0001 5br n = 543 DMSO 0.01% vs. 5bt < 0.0001 5bs n = 1250 5bt n = 914 FIG. 3B Calcium imaging - One-way ANOVA Dunnett’s multiple comparisons test DMSO 0.01% screening with a 90 mM p < 0.0001 DMSO 0.01% vs. 5aa < 0.0001 n = 1032 KCl challenge DMSO 0.01% vs. 5ab < 0.0001 5aa n = 378 DMSO 0.01% vs. 5ac < 0.0001 5ab n = 995 DMSO 0.01% vs. 5ad < 0.0001 5ac n = 471 DMSO 0.01% vs. 5ae < 0.0001 5ad n = 200 DMSO 0.01% vs. 5af < 0.0001 5ae n = 554 DMSO 0.01% vs. 5ag < 0.0001 5af n = 244 DMSO 0.01% vs. 5ah 0.3379 5ag n = 242 DMSO 0.01% vs. 5ai < 0.0001 5ah n = 275 DMSO 0.01% vs. 5aj < 0.0001 5ai n = 542 DMSO 0.01% vs. 5ak < 0.0001 5aj n = 409 DMSO 0.01% vs. 5al < 0.0001 5ak n = 214 DMSO 0.01% vs. 5am 0.0086 5al n = 590 DMSO 0.01% vs. 5an 0.0086 5am n = 216 DMSO 0.01% vs. 5ao < 0.0001 5an n = 437 DMSO 0.01% vs. 5ap 0.9803 5ao n = 567 DMSO 0.01% vs. 5aq 0.7626 5ap n = 222 DMSO 0.01% vs. 5ar 0.3921 5aq n = 683 DMSO 0.01% vs. 5as 0.9997 5ar n = 455 DMSO 0.01% vs. 5at < 0.0001 5as n = 357 DMSO 0.01% vs. 5au 0.9984 5at n = 934 DMSO 0.01% vs. 5av < 0.0001 5au n = 885 DMSO 0.01% vs. 5aw < 0.0001 5av n = 534 DMSO 0.01% vs. 5ax < 0.0001 5aw n = 264 DMSO 0.01% vs. 5ay < 0.0001 5ax n = 597 DMSO 0.01% vs. 5az < 0.0001 5ay n = 852 DMSO 0.01% vs. 5ba < 0.0001 5az n = 1132 DMSO 0.01% vs. 5bb 0.0046 5ba n = 802 DMSO 0.01% vs. 5bc 0.285 5bb n = 567 DMSO 0.01% vs. 5bd < 0.0001 5bc n = 530 DMSO 0.01% vs. 5be 0.9988 5bd n=751 DMSO 0.01% vs. 5bf 0.0577 5be n = 348 DMSO 0.01% vs. 5bg < 0.0001 5bf n = 284 DMSO 0.01% vs. 5bh < 0.0001 5bg n = 747 DMSO 0.01% vs. 5bi < 0.0001 5bh n = 802 DMS0 0.01% vs. 5bj 0.0564 5bi n = 644 DMSO 0.01% vs. 5bk < 0.0001 5bj n = 95 DMSO 0.01% vs. 5bl < 0.0001 5bk n = 78 DMSO 0.01% vs. 5bm < 0.0001 5bl n = 958 DMSO 0.01% vs. 5bn 0.0007 5bm n = 381 DMSO 0.01% vs. 5bo < 0.0001 5bn n = 100 DMSO 0.01% vs. 5bp < 0.0001 5bo n = 559 DMSO 0.01% vs. 5bq < 0.0001 5bp n = 604 DMSO 0.01% vs. 5br < 0.0001 5bq n = 681 DMSO 0.01% vs. 5bs < 0.0001 5br n = 543 DMSO 0.01% vs. 5bt < 0.0001 5bs n = 1250 5bt n = 914 FIG. 3D Calcium imaging - time One-way ANOVA Dunnett’s multiple comparisons test DMSO 0.01% course of effect of 5bk p < 0.0001 DMSO 0.01% vs. Acute p = 0.1863 n = 87 DMSO 0.01% vs. 30 min p = 0.0043 Acute 5bk n = DMSO 0.01% vs. 3 hrp < 0.0001 108 DMSO 0.01% vs. overnight p < 30 min 5bk n = 0.0001 81 3 hr 5bk n = 75 overnight 5 bk n = 128 FIG. 3E Calcium imaging - Non-linear [Inhibitor] vs. response (three concentration response of regression parameters) 5bk IC50 = 4.195 μM; r² = 0.4137 FIG. 5C Whole cell patch clamp Unpaired t-test DMSO 0.01% electrophysiology - Peak T DMSO 0.01% vs. 5bk 20 μM n = 16 type currents p = 0.2343 (V_(0.5)) and p = 0.1009 (k) 5bk n = 16 FIG. 5D Whole cell patch clamp Non-parametric Mann-Whitney test DMSO 0.01% electrophysiology - test V_(0.5): DMSO 0.01% vs. 5bk 20 μM n = 16 Voltage-dependence of p = 0.0019 5bk n = 16 half-activation (V_(0.5)) and slope (k) FIG. 5F Whole cell patch clamp Mann-Whitney test DMSO 0.01% electrophysiology - DMSO 0.01% vs. 5bk 20 μM n = 8 _(τinactivation) p = 0.9591 5bk n = 8 FIG. 5H Whole cell patch clamp Mann-Whitney test DMSO 0.01% electrophysiology - 0-90% DMSO 0.01% vs. 5bk 20 μM n = 17 rise time at −40 mV p = 0.3292 5bk n = 19 FIG. 5I Whole cell patch clamp Unpaired t-test DMSO 0.01% electrophysiology - DMSO 0.01% vs. 5bk 20 μM n = 15 Voltage-dependence of p = 0.7833 (V_(0.5)) and p = 0.0575 (k) 5bk n = 16 half-inactivation (V_(0.5)) and slope (k) FIG. 6D Whole cell patch clamp Mann-Whitney test DMSO 0.01% electrophysiology - Peak L DMSO 0.01% vs. 5bk 20 μM n = 10 type currents p = 0.4470 5bk n = 9 FIG. 6E Whole cell patch clamp Mann-Whitney test DMSO 0.01% electrophysiology - DMSO 0.01% vs. 5bk 20 μM n = 10 Voltage-dependence of p = 0.2222 (for Activation V_(0.5)) 5bk n = 9 half-activation and DMSO 0.01% vs. 5bk 20 μM inactivation (V_(0.5)) and p = 0.9318 (for Activation A:) slopes (k) of L-type DMSO 0.01% vs. 5bk 20 μM currents p = 0.2222 (for Inactivation V_(0.5)) DMSO 0.01% vs. 5bk 20 μM p = 0.4862 (for Inactivationk) FIG. 6I Whole cell patch clamp Mann-Whitney test DMSO 0.01% electrophysiology - Peak DMSO 0.01% vs. 5bk 20 μM n = 12 P/Q type currents p = 0.8992 5bk n = 12 FIG. 6J Whole cell patch clamp Mann-Whitney test DMSO 0.01% electrophysiology - DMSO 0.01% vs. 5bk 20 μM n = 10 Voltage-dependence of p = 0.2496 (for Activation V_(0.5)) 5bk n = 8 half-activation and DMSO 0.01% vs. 5bk 20 μM inactivation (V_(0.5)) and p = 0.0694 (for Activation k) slopes (k) of P/Q-type DMSO 0.01% vs. 5bk 20 μM currents p = 0.2017 (for Inactivation V_(0.5)) DMSO 0.01% vs. 5bk 20 μM p = 0.3637 (for Inactivation k) FIG. 6N Whole cell patch clamp Mann-Whitney test DMSO 0.01% electrophysiology - Peak DMSO 0.01% vs. 5bk 20 μM n = 14 N type currents p = 0.2575 5bk n = 12 FIG. 6O Whole cell patch clamp Mann-Whitney test DMSO 0.01% electrophysiology - DMSO 0.01% vs. 5bk 20 μM n = 12 Voltage-dependence of p = 0.5003 (for Activation V_(0.5)) 5bk n = 17 half-activation and DMSO 0.01% vs. 5bk 20 μM inactivation (V_(0.5)) and p = 0.8481 (for Activation k) slopes (k) of N-type DMSO 0.01% vs. 5bk 20 μM currents p = 0.0930 (for Inactivation V_(0.5)) DMSO 0.01% vs. 5bk 20 μM p = 0.2784 (for Inactivationk) FIG. 6S Whole cell patch clamp Mann-Whitney test DMSO 0.01% electrophysiology - Peak DMSO 0.01% vs. 5bk 20 μM n = 14 R type currents p = 0.6830 5bk n = 15 FIG. 6T Whole cell patch clamp Mann-Whitney test DMSO 0.01% electrophysiology - DMSO 0.01% vs. 5bk 20 μM n = 14 Voltage-dependence of p = 0.7532 (for Activation V_(0.5)) 5bk n = 15 half-activation and DMSO 0.01% vs. 5bk 20 μM inactivation (V_(0.5)) and p = 0.5951 (for Activation k) slopes (k) of R type DMSO 0.01% vs. 5bk 20 μM currents p = 0.9038 (for Inactivation V_(0.5)) DMSO 0.01% vs. 5bk 20 μM p = 0.8727 (for Inactivation k) FIG. 9 Calcium imaging Non-parametric Mann-Whitney test Scramble test Scramble DMSO vs. Scramble DMSO n = 42 5bk p = 0.0132 Scramble 5bk siRNA CaV3.1 DMSO vs. siRNA n = 17 CaV3.1 5bk p = 0.0040 siRNA CaV3.1 siRNA CaV3.2 DMSO vs. siRNA DMSO n = 19 CaV3.2 5bk p = 0.6277 siRNA CaV3.1 siRNA CaV3.3 DMSO vs. siRNA 5bk n = 13 CaV3.3 5bk p = 0.0469 siRNA CaV3.2 DMSO n = 10 siRNA CaV3.2 5bk n = 12 siRNA CaV3.3 DMSO n = 24 siRNA CaV3.3 5bk n = 17 FIG. 10C Constellation z-test DMSO 0.01% vs. 5bk 20 μM pharmacology - # of P = 0.00288 functional classes FIG. 10D Constellation z-test DMSO 0.01% vs. 5bk 20 μM DMSO 0.01% pharmacology - % 1 response: p = 0.02144 n = 2002 cells responders 2 response: p = 0.63122 5bk 20 μM 3 response: p = 0.48392 n = 2902 cells 4 response: p = 0.65994 5 response: p = 0.60306 6 response: p = 0.98404 FIG. 10E Constellation z-test DMSO 0.01% vs. 5bk 20 μM DMSO 0.01% pharmacology - % AITC: p = 0.41222 n = 2002 cells responders Acetylcholine: p = 0.23404 5bk 20 μM ATP: p < 0.00001 n = 2902 cells Histamine: p = 0.77948 Menthol: p = 0.10524 Capsaicin: p < 0.00001 FIG. 10F Constellation z-test DMSO 0.01% vs. 5bk 20 μM DMSO 0.01% pharmacology - average ACh/ATP: p = 0.5552 n = 2002 cells peak response ACh/Cap: p = 0.90448 5bk 20 μM ATP/Menthol: p = 0.79486 n = 2902 cells Menthol/Cap: p = 0.98404 AITC/ATP/Cap: p = 0.86502 ACh/ATP/Cap: p = 0.80258 ATP/Menthol/Cap: p = 0.84148 AITC/ATP/Menthol/ Cap: p = 0.8807 FIG. 10G P Constellation Mann-Whitney DMSO 0.01% vs. 5bk 20 μM DMSO 0.01% pharmacology - Peak AITC: p = 0.017 n = 2002 cells response to trigger Acetylcholine: p = 0.0035 5bk 20 μM ATP: p < 0.0001 n = 2902 cells Histamine: p = 0.6790 Menthol: p < 0.0001 Capsaicin: p < 0.0001 KCl: p < 0.0001 FIG. 10H Constellation Mann-Whitney DMSO 0.01% vs. 5bk 20 μM DMSO 0.01% pharmacology - area under AITC: p < 0.0001 n = 2002 cells the curve Acetylcholine: p = 0.0002 5bk 20 μM ATP: p = 0.0434 n = 2902 cells Histamine: p = 0.0131 Menthol: p = 0.0001 Capsaicin: p = 0.9615 FIG. 10I Constellation Mann-Whitney DMSO 0.01% vs. 5bk 20 μM DMSO 0.01% pharmacology - Average AITC: p = 0.2493 n = 2002 cells Peak KCl response Acetylcholine: p < 0.0001 5bk 20 μM ATP: p < 0.0001 n = 2902 cells Histamine: p = 0.3729 Menthol: p < 0.0001 Capsaicin: p < 0.0001 KCl: p < 0.0001 FIG. 13A-C Competition Binding 3 variable, 1 site 5bk was reported as “Not Converged” Results in Assay for Mu, Delta, and binding non-linear for all 3 panels, meaning no measure of Kappa opioid receptors regression curve- measurable competition. affinity fit Mathematically, this is defined as no reported as fitted curve with an R² > 0.6. mean Ki ± SEM of the N = 3 set. FIG. 14B Slice electrophysiology - Mann-Whitney Control Control (DMSO 0.01%): Amplitude of EPSCs p = 0.4332 (DMSO n = 1 0.01%): n = 17 5bk (20 μM): n = 1 5bk (20 μM): n = 17 FIG. 14C Slice electrophysiology - Mann-Whitney Control Frequency of EPSCs p < 0.0001 (DMSO 0.01%): n = 17 5bk (20 μM): n = 18 FIG. 15 CGRP release from spinal Two-way Dunnett’s multiple comparisons test DMSO 0.01% cords ANOVA Baseline 1: DMSO 0.01% vs. 5bk n = 4 20 μM p = 0.9998 5bk n = 4 for Baseline 2: DMSO 0.01% vs. 5bk all conditions 20 μM p = 0.9935 Treatment: DMSO 0.01% vs. 5bk 20 μM p = 0.9994 Treatment plus 90 mM KCl: DMSO 0.01% vs. 5bk 20 μM p = 0.0002 Wash: DMSO 0.01% vs. 5bk 20 μM p = 0.8947 FIG. 16A Spared nerve injury - paw Two-way Sidak’s post hoc test Vehicle n = 6 withdrawal threshold ANOVA Vehicle vs. 5 bk: 5bk n = 6 Pre: p > 0.9999 for all   0 min: p > 0.9999 conditions  30 min: p > 0.9999  60 min: p > 0.9999 120 min: p = 0.0150 180 min: p = 0.0162 240 min: p = 0.0828 300 min: p = 0.9074 FIG. 16B Spared nerve injury - % Two-way Sidak’s post hoc test Vehicle n = 6 anti-allodynia ANOVA Vehicle vs. 5 bk: 5bk n = 6  30 min: p > 0.9999 for all  60 min: p > 0.9999 conditions 120 min: p = 0.0344 180 min: p = 0.0341 240 min: p = 0.1245 300 min: p = 0.8773 FIG. 16C Spared nerve injury - Area Mann Whitney test Vehicle n = 6 under the curve Vehicle vs. 5 bk p = 0.0411 5bk n = 6 for all conditions FIG. 16D GP120 - paw withdrawal Two-way Sidak’s multiple comparisons Vehicle n = 6 threshold ANOVA post hoc test 5bk n = 6 Vehicle vs. 5 bk: for all Pre: p > 0.9999 conditions   0 min: p > 0.9999  30 min: p = 0.9998  60 min: p = 0.0022 120 min: p = 0.0002 180 min: p = 0.0208 240 min: p = 0.7186 300 min: p = 0.6802 FIG. 16E GP120 - % anti-allodynia Two-way Sidak’s multiple comparisons Vehicle n = 6 ANOVA post hoc test 5bk n = 6 Vehicle vs. 5 bk: for all  30 min: p = 0.9908 conditions  60 min: p = 0.0060 120 min: p = 0.0015 180 min: p = 0.0422 240 min: p = 0.9751 300 min: p = 0.8785 FIG. 16F GP120 - Area under the Mann Whitney test Vehicle n = 6 curve Vehicle vs. 5 bk p = 0.0152 5bk n = 6 for all conditions FIG. 16G Paclitaxel - paw Two-way Sidak’s multiple comparisons Vehicle n = 6 withdrawal threshold ANOVA post hoc test 5bk n = 6 Vehicle vs. 5 bk: for all Pre: p > 0.9999 conditions   0 min: p > 0.9999  30 min: p = 0.9994  60 min: p > 0.9999 120 min: p = 0.0042 180 min: p = 0.0009 240 min: p = 0.0248 300 min: p >0.9999 FIG. 16H Paclitaxel nerve injury - % Two-way Sidak’s multiple comparisons Vehicle n = 6 anti-allodynia ANOVA post hoc test 5bk n = 6 Vehicle vs. 5 bk: for all  30 min: p = 0.9989 conditions  60 min: p = 0.9996 120 min: p = 0.0134 180 min: p = 0.0040 240 min: p = 0.0346 300 min: p = 0.9912 FIG. 161 Paclitaxel nerve injury - Mann Whitney test Vehicle n = 6 Area under the curve Vehicle vs. 5 bk p = 0.0260 5bk n = 6 FIG. 17A Rotarod Two-way Sidak’s multiple comparisons Vehicle n = 6 ANOVA post hoc test 5bk n = 6 Vehicle vs. 5 bk: for all Pre: p > 0.9999 conditions  30 min: p = 0.9999  60 min: p = 0.9995 120 min: p = 0.9893 180 min: p >0.9999 240 min: p = 0.9960 300 min: p >0.9999 FIG. 17B Anxiety (elevated plus Mann-Whitney Vehicle n = 7 maze) p = 0.6230 5bk n = 7

INCORPORATION BY REFERENCE

The entire disclosure of each of the patent documents and scientific articles referred to herein is incorporated by reference for all purposes. The following references are herein incorporated by reference in their entireties:

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Equivalents

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting the invention described herein. Scope of the invention is thus indicated by the appended claims rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein. 

1. A compound encompassed within:

including pharmaceutically acceptable salts, solvates, and/or prodrugs thereof, wherein each of X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound to inhibit CaV3.2 voltage gated calcium channel activity.
 2. The compound of claim 1, wherein each of X, R1, R2, and R3 independently include any chemical moiety that permits the resulting compound capable of one or more of the following: inhibiting depolarization-induced calcium influx related to CaV3.2 voltage gated calcium channel activity; inhibiting, preventing and/or ameliorating neuropathy pain related to CaV3.2 activity; inhibiting, preventing and/or ameliorating pain related to CaV3.2 activity; inhibiting, preventing and/or ameliorating pain related to HIV-associated peripheral sensory neuropathy; inhibiting, preventing and/or ameliorating pain related to chemotherapy-induced peripheral neuropathy (CIPN); inhibiting, preventing and/or ameliorating pain related to spinal nerve ligation (SNL) induced neuropathy; inhibiting spontaneous excitatory post-synaptic currents via actions presynaptically; and inhibiting release of the pronociceptive neurotransmitter calcitonin gene related peptide (CGRP).
 3. The compound of claim 1, wherein X is C thereby rendering the compound a piperidine based compound.
 4. The compound of claim 1, X is N thereby rendering the compound a piperazine based compound.
 5. The compound of claim 1, wherein R1 is selected from


6. The compound of claim 1, wherein R2 is selected from


7. The compound of claim 1, wherein R3 is selected from


8. The compound of claim 1, wherein the compound is recited in FIG. 1B with the exception of Compound 5-aa.
 9. A pharmaceutical composition comprising a compound of claim
 1. 10. A method of treating, ameliorating, or preventing a condition related to CaV3.2 activity in a patient comprising administering to said patient a therapeutically effective amount of the pharmaceutical composition of claim
 9. 11. The method of claim 10, wherein said condition related to CaV3.2 activity is one or more of pain related to general neuropathy; pain related to diabetes related neuropathy; pain related to HIV-associated peripheral sensory neuropathy; pain related to chemotherapy-induced peripheral neuropathy (CIPN); pain related to spinal nerve ligation (SNL) induced neuropathy, and pain related to CaV3.2 activity.
 12. The method of claim 10, wherein said patient is a human patient.
 13. The method of claim 10, further comprising administering to said patient one or more agents for treating pain. 14-25. (canceled) 